Is it worth bidding differently by time of day?

Yes, if one stretch brings calls and another only clicks while the venue is full or shut. It is not worth splitting the day into eight slots with so little data that each one is an anecdote. Look at calls by hour over two weeks, not one Saturday. Adjust only the stretch that repeats. The bid is lowered at lunch because “there are fewer clicks”, and that was exactly when the booking phone rang. The change was made on the wrong chart. Two stretches at most: the gap at a normal bid, and full or closed on pause. It is reviewed against the floor sheet, not against impressions.