I could have sworn I heard keep schedule on a television show where two people were talking informally about making appointments despite last-minute hiccups. But I can't find the phrase anywhere on the internet. "Keep to schedule", or "stay on schedule" seem to be the acceptable forms among a few others. Can I use to keep schedule to mean making all prearranged appointments and going as planned without disruptions?
The phrase keep schedule refers to staying on schedule.
It would be well within the Shetland's ability to fly a strong headwind from Cairo to Poole, and also keep schedule as demonstrated in Chart 8. link
...Manila Railroad Company (failure to keep schedule) link
In Kansas City they were told that the Interstate Trail had brought them that far, but from there south they would bump into troubles they never dreamed of and that it would be impossible to keep schedule if they could keep going at all. link
When you do impose a fine in the rather exceptional and unusual cases on one of these important trains for failure to keep schedule, does that fine not come out of the pocket of the railroad? link
I think it would be fair to say that it is a somewhat dated use.