hie, why does my dog lately lip lick at a certain time in a day around 10-11 am in the morning and once at night...

Hi Kriss. This behaviour shown by dogs mainly when they are confused or stressed or frustrated. But that isn’t the reason all the time, it also happens when a pet has any sort of sickness/dental issues or ulcers in the mouth/ when being nauseated . Overall check him to rule out above said conditions. Calm him down by spending extra time with him (play with him, especially during times you mentioned) or by giving treats. Get him thoroughly checked by a vet as well.