I'm not sure why it matters if you start checking time when the script is loaded. If you don't do that, then there will be 0 uptime until you exit and restart mIRC, which seems like a bad way to handle that.
on LOAD sets your fixed variable. on START sets your other variable that gives you your uptime from the time mIRC starts, but also gives you something to use from the first time the script is loaded without having to restart mIRC to make it work. That certainly sounds like how it should work, and that's what it does.
I just don't see why you'd want it to not start providing uptime as soon as the script is loaded without having to restart mIRC first.
