There were no times noted for Monday, I assumed that meant they were closed so I removed the Monday part of the tag.

Upon further research I found 2 different websites, both belonging to this restaurant. One of them says they're open 7 days a week and the other says they're closed on Tuesdays. I'm not sure which to believe.

http://www.theoldsiam.org/
https://theoldsiam.net/about-us/