Hi,
Time as in the camera time during the night? If so then simply farm glass metal and plastic (forgot which two actually are needed for the upgrade) and in-between nights, when you're on the PC screen (icons like shop, cam, stats, etc.) go to cam and on the other tab you'll see 4 possible upgrades (lens - more credits, SD card - more time, x-ray - well...x-ray, and 4th that substitutes rizz aura perks) focus on SD card which will increase your time.
Remember, that besides the camera time there's also your stamina (battery life during the night) that has an impact on the night length, keep doing runs to increase the stamina.
TL;DR
Upgrade SD card in cam menu accessed from PC, by farming plastic/glass/metal during runs and run a lot to increase stamina (battery life).
As for max time you can farm it to the max available so 99 minutes (I don't think anyone is crazy enough to actually do that)
Hope this helps,
Cheers