If you are playing and your phone or tablet goes idle or the screen shuts off, then the game will stop counting time. So if you want to let the game sit for awhile and rack up DNA for you while you aren’t doing anything, then go to the settings on your phone or tablet and shut off the auto-lock feature on your iPhone or iPad. This will be under “general” in your device’s settings.
Of course, this progression will automatically be stopped whenever one of the game’s notifications pop up. The best time to do this, then, is to wait until a couple years in the game have passed and then set your phone or tablet down and let it sit and collect DNA for you. You can also do this after everybody has already been infected, since there will be no notifications by then until people start dying. Even then, newscasts will sometimes pop up with random notifications, too.
If you haven’t managed to infect every country yet but you have already let loose the symptoms, and countries are starting to block off transportation and other forms of spreading the disease, you’ll still be able to salvage the win, you just have to spend DNA as quickly as you get them. You’ll have to spread the DNA evenly between transmission methods, symptoms, and blocking the research. However, if you don’t do it quickly enough, the cure could be evenly spread before you’re done. If that happens, simply start over and let the disease spread to every country first.
If you make the mistake of purchasing all of the research blockers first, that’s more easily salvageable, though. You can still win just by waiting to purchase the symptoms, saving up your DNA by waiting it out. You’ll save up DNA faster if you let the disease spread slowly, since DNA slows down after infections stop. But if you have already infected everybody AND purchased the research blockers, simply put the game into double speed mode and wait for the DNA to build up.
If you’re patient, then leave the game in normal speed, rather than double speed, because you will earn DNA faster (relative to the amount of time that has passed) in normal than double speed.