Timing (relatively) long events

Hmm ok, thanks for that. I think datetime could work, but do you know what happens if you start it up without setting the clock? Will it just start from January 1 1900? That's fine, I'm not interested in the date being kept, just the amount of time that has passed. But if the clock needs to be "turned on" somehow then I'm not sure if it's gonna work, because I have no way to set it...