They usually leave after the opening statements and then come back just before it is their turn. C-Span occasionally shows the seats, empty but for a few.
This does kinda remind me of the SAT...hours of torture, then a 5-minute break, then more hours...
Only for the witnesses. Remember the Senators are often not there. They can have a meal, take a nap, use the restroom, etc. Not so the witnesses. Senators think that they are gods.
And that MUST change! We PAY them to represent US!
I say..... clear the board and start over.