"Are they open now" is one of the most common things anyone asks about a local business, and it is one of the few facts an AI can state about you with confidence, if you give it one. A straight answer is what lets you be recommended at four on a Sunday.
Fill in all seven days
A blank day does not read as closed. It reads as unknown, which is worse than either answer, and it makes anything summarising your availability hedge. Mark the days you are shut as closed rather than leaving them empty.
If you work by appointment, set the hours you answer the phone. That is the question people are really asking when they look.
Special hours
Add special hours for bank holidays when they come around. That is the moment somebody checks and the moment a wrong answer costs you the job. Google prompts you for the big ones a week or two ahead, and that prompt is worth acting on rather than dismissing.
What it is worth
The finding prints what it is worth on your scan as X of Y points within Local presence. Partly filled in is a warning rather than a failure, so completing it moves you less than starting from nothing would. It takes five minutes either way.