Congratulations.
Never any harm in asking.
Certainly before you sign, which focuses minds and can be in your contract, in black and white.
My friend had great flexibility, but not in her contract, and then a new Head arrived and was difficult about it.
It was annoying.
After a remark that annoyed her in front of others about her leaving early, she spoke to a friend in recruitment and through pure luck had a great offer of a new job within days.
Super flexible and 10k more.
Timing and luck.
She was thrilled.
She quickly resigned and because of having so much leave she was gone in 10 working days.
They were not happy and her Project Manager on her current project, told her they were very disappointed that she hadn't told them she was unhappy.
She said she wasn't unhappy at all, but the new Head's disrespect of her long standing flexible arrangement and public remarks, was the push, and it had now landed her a new great flexible position so it had all worked out.
The Project Manager was very pissed and it became a thing.
She left as planned but was told her position was there if she ever wanted it, they would match her increase and flexibility would be written in.
She has gone from one hours travel to 25 minutes and she said that of itself has been transformative to her life.
Best of luck OP.
Flexibility is priceless when you have children.