This has been asked almost ad-nausea. Many discussions about shows starting/ending 1 minute before/past the hour.
Finally got TabloTV to answer why it’s not, or very unlikely to happen - 7:01 8:31 9:01 etc - #35 by TabloTV
We were trying to limit the number of options available in order to keep things simple. We felt that the 2 minute option would cover the most use cases.
FYI: there is a third party app - APL Tablo Client which allows you to set start and end times by the +/- as desired.