Hello and welcome!
I personally believe that downtime is quite important. It can be very difficult to strike the right balance between feeling that you've done enough (which you probably will never feel) and not doing enough.
What we did last year was we made sure that dd had one full day every week (during term time) where she didn't do any work at all. She worked most days during the half terms and the Easter holiday as well. We kept to our one day a week of no work. During the summer holidays we felt that she really needed a complete rest so we took the first week of the holidays off and went away. No work was done that week and no one was allowed to mention the 11+!
After that it was back to our working 6 days out of 7 routine. Unfortunately, I work so dd had to go to child care during the holidays which meant that she only did about about 2 hours of 11+ work per day, I would have preferred for her to do 4 hours a day but it wasn't an option.
We also took the bank holiday weekend in August off and went away but dd still did 2 hours of 11+ work each day over that weekend, we took it with us!
When we went back to school after the summer, we stuck with our 6 days out of 7 routine and she did a couple of hours every day after school. The Friday before the exam was spent doing nothing. She went to school as usual but she just came home and relaxed afterward. My feeling was that if she didn't know it by then, she would never know it.
It's not easy deciding what is enough and what's too much but I am reasonably happy that we got it almost right.