PT Hours - When to ask for a reduction from FT

[okitoki]

Hello,

I have been in my current full time role for 3 years but in the last 6 months reduced my hours to 4 full days.

I’m loving that one day off which is all mine.

I have applied for a full time role at another company same industry and it looks as if I may be invited to interview.

My question, when would it be appropriate to negotiate 5 days to 4?

I doubt the interview, perhaps in my acceptance of the role? Once I have actually started may be too late as HR would have already set up payroll and it’d be an inconvenience to make changes so soon, but if they reject my offer I may not last out the probation period as they may doubt my dedication? Should I wait until after my probation period when they’ve had the chance to realise they cannot live without me, lol?

To work 5 days would not be a deal breaker but I’d really prefer not to.