Dead Rising/Overtime Mode

Overtime Mode is significantly more difficult than 72 Hour Mode, thanks to the number of Special Forces troops around, and the much tighter time restriction on your activities. It's worth at least unlocking the Real Mega Blaster (awarded for getting the Zombie Genocider achievement), and there's a lot to be said for making it all the way to level 50 as well.

Overtime Mode
Just when all hope seems lost, Isabela appears on the roof. She kills the zombies around Frank, but as she approaches him he collapses and passes out.

Several hours later, he wakes up back in Carlito's Hideout. His fainting is a bad sign, though - it means he's been infected and will soon turn into a zombie. Isabela is hopeful, suggesting that he seems to have a high level of resistance to the virus, but Frank doesn't seem so optimistic. With Ed's helicopter having crashed, he's just about ready to give up.

Isabela has a plan though, and thinks she might be able to postpone the zombification process even more than Frank's immune system can on its own. She'll need you to collect a number of supplies in order to create a serum that will slow the virus down.

You've got 24 hours to get everything she needs for the serum before Frank becomes a zombie.

Method To Prevent Infection
There are eight items that she needs you to gather, but the order they appear in your mission select list isn't the most efficient. The route below requires you to have rescued Greg on the first day and have picked up the maintenance tunnel key at some point; the shortcuts offered by these optional items make crossing the mall much easier - especially since the Special Forces are back again, and this time they have a fancy new toy.

Leave the hideout and head up to the main area of North Plaza to get a glimpse of it: a small helicopter with a mean gun and a loud alarm. If one catches site of you, it'll call in a lot of backup from the Special Forces, as well as taking its own pot-shots at you. Luckily, their rotors are fairly noisy, so you can hear them before they spot Frank. They tend to move pretty slowly as well, so if you've got a sniper rifle then they're pretty easy to take out - and you'll get a 500PP bonus for each one.

Isabela's List
The things Isabela has asked for, as listed in the game, are: She's also asked for an unspecified number of Queens, but you've got enough to worry about with this lot for now.
 * Cold Spray - SporTrance, Paradise Plaza
 * First Aid Kit - Seon's Food and Stuff, North Plaza
 * Blender - Food Court, or Columbian Roastmasters, Paradise Plaza
 * Coffee Filters - Security Room
 * Magnifying Glass - Wonder Jewels, Wonderland Plaza
 * Camp Stove - Sports High, Entrance Plaza
 * Developing Solution - Cam's Camera, Paradise Plaza
 * Perfume Bottle - Estelle's Fine-lady Cosmetics, Entrance Plaza

The first item on the list to get is the First Aid Kit, which you'll find the Pharmacy in Seon's. It's on the shelves next to where the medicine was in Medicine Run. The supermarket is crawling with Special Forces though, so be careful. You should also take the opportunity to stock up on health items; wine, located next to the pharmacy counter, is the best option.

Once you've picked up the First Aid Kit, don't go back into Seon's; instead, take the stairs down to the maintenance tunnels and hop into the van down there. From here, drive down to the Entrance Plaza - you'll come out between Children's Castle and Everyone Luvs Books. Head over to the other side and down to the left to find Sports High; the Camp Stove is on a set of stand-alone shelving units near the door.

Head back out into the Entrance Plaza and up the stairs nearest you, then follow the upper walkway along to the north end of the Entrance Plaza. Use the stores for cover, and keep an ear out for the mini-choppers; there's usually one floating around each end of the Plaza. At the top end, you'll find the Perfume Bottle in Estelle's Fine-lady Cosmetics, on the rear corner of the central pillar.

Stay on the top level of the Entrance Plaza and go back down the opposite side than the one you came up on, and then head through the side door to the Security Room, which will now let you through. If you've got the Real Mega Blaster or the Real Energy Sword, you should drop them just before leaving the Entrance Plaza so you can pick up fresh weapons in the Security Room.

The Coffee Filters are on the desk in front of the security monitors - and while you're here it's a good time to save, since you're halfway through Isabela's list.

Take the airvents out onto the Rooftop and then head into the Warehouse. Taking the door onto the shelves is a little easier since the Special Forces on the ground won't be able to shoot up at you, but there are a couple of them on the shelves themselves that you'll have to contend with. Go out into Paradise Plaza and into Cam's Camera right beside the Warehouse door, where you'll pick up the Developing Solution behind the counter.

Head upstairs and pick up the Cold Spray just inside the door of SporTrance, then go across the corridor and into Columbian Roastmasters for health and the Blender Isabela's asked for. The final item on the list is in Wonderland Plaza, so head down the stairs between SporTrance and Lady About Town and into the ladies' bathrooms to take the shortcut across, and another opportunity to save.

Wonder Gems is directly across from the bathrooms in Wonderland Plaza, and the Magnifying Glass is on a counter near the back of the store. With everything now in your posession, head into North Plaza and back to Carlito's Hideout - you can use Isabela's motorcycle, parked outside Seon's, if you need to hurry.

Back at the hideout, speak to Isabela to hand over the goodies. She's made the serums before, although in lab conditions and with a synthesised version of the zombie hormone she's planning to extract from queens, but confesses that she can't guarantee how long this stop-gap measure will hold off Frank's infection.

Despairing at his future as a zombie timebomb, Frank reminds Isabela about a chilling idea: Carlito may have used a war orphan charity he was involved with to send infected children across America, with a version of Isabela's serum holding the zombie virus in check temporarily. However, since they're currently stuck in Wilamette with no way out, the best option at the moment is to deal with Frank's infection, and worry about the outside world when they get to it.

Generator
When the cutscene ends, speak to Isabela again. This time, the generator's stopped working, and she'll need a replacement. Carlito used the clock tower in the Leisure Park as storage, so there might be a replacement in that area.