Originally Posted by AlanB

My understanding of things is that it is not time based. When the conductors finish their sweep of the train collecting/scanning tickets, they hit a button in the App that closes out the batch, as it were, from that station. Once that happens, if you didn't board at your assigned station your reservation is cancelled.

So the question becomes, can the conductors sweep the entire train in between Route 128 & Providence? My best guess is that on a day when the train is running full, they won't complete before PVD. But with a light passenger load, they may well complete before PVD and you could be in trouble.