Well spotted, I am aware of the problem, here's how it worked when I started it.
1) A FB link is added, all of the info is checked in the background and opening times will be displayed if it finds them.
2) For every FB link in the system (About 35,000 of them I think) they would be rechecked once every day and opening hours updated or added if there were none before.
3) Opening hours are only displayed on PG if they have been rechecked within the last 24 hours to try to avoid out of date info.
Sadly since the whole Cambridge Analytica stuff earlier in the year Facebook have severely restricted access to data. So in the last 24 hours only around 500 pubs have been rechecked so opening times wont be displaying on the other 34,500.
I'm working on improving this as it is very frustrating but it is possible Facebook may remove my access to the data entirely, their processes are very unclear.