My cell phone only handles countdowns up to one hour, and the standard kitchen timer has the same limitation.
I wanted to set a timer for three and a half hours. My computer does everything else, so I Googled how to set a timer in Windows 10. And there it was, I can set multiple timers for up to twenty-three hours, fifty-nine minutes and fifty-nine seconds. Yay!
Click the Windows symbol in the bottom left corner, click Alarms and Clock, select Timer from the top, and click the plus sign at the bottom, then choose the number of hours, minutes and seconds you want. Other versions of Windows may have something similar. To find out, Google “how to set timers in Windows <version>.