Lucy and Flora did full days in their crates, and they were fine. We had a few rules, however.
They could not be in the crates for more than 8 hours. My husband and I staggered our start times at work to ensure this would be the case.
They got lots of exercise morning and evening.
We bought each of them a kong, and stuffed their breakfasts in them. That gave them a project for at least part of the day.
After my first maternity leave, they got the run of the house. After being home with them for that long, I knew they mostly just did napping tours of the house.