as a travel agent - yes, this does sound normal. i recieve several and flight time changes can be anything from a few mins upwards. american internal flights are the worst, because they can be so precise (where we in the uk use flight times that end in either 5 or 0 - 05,10,15,20 etc..... the americans tend to be precise to the minute eg dept 12:56 arr 18:21)
effectively, a 1 minute change can generate a notification.