Zippy, what happened to you is probably due to an unfortunate occurrence, but many fellow pilots just don't care about losing a CTOT even when it's pretty clear to them, they will just let it expire to get a new one later , this is not a problem for the ATC operations but it's not fair 'cause someone else, somewhere else, should be able to use your slot, one day (it already happened for sure and you don't know) you will spend some more time on the tarmac because of one of this guys.
Another thing to clarify is that you don't have a window, the window is exclusively meant for ATC use, if your CTOT was at 1200 at time 1212 you missed it by 12 minutes, not 2.