Most childminders working unsocial hours are doing so on top of a normal 50 hour week. On top of which they've got to fit in all the "behind the scenes" jobs of doing accounts, all the admin, planning, cleaning & checking toys & equipment, meetings with parents, training etc etc. Which leaves precious little time for your own family as it is.
So commonly, the charges for unsocial hours (before 8 am/after 6pm & Bank Holidays) - double time and for Sats/Suns - Time & a Half (some charge double time on Sundays).
Some have come to other arrangements eg charging normal rates for up to 10-12 hours a day and the unsocial rate only applies to those booking more than that each day. This is helpful for those parents who are not being paid an over time rate for working these hours themselves.
Don't know anyone here who does overnight anymore (about 10 years ago used to be £15-20 a night). According to posts I've seen on various forums childminders are charging £35-£70 per night, most charge around £45-55.
If you are registered with Ofsted, always suggest to parents they they check their entitlement to the childcare element of tax credits - if eligible they can claim up to 80% of your fees. If they don't qualify for that, childcare vouchers will save them a little money as each parent can be paid up to £243 a month in the form of childcare vouchers instead of ££££££. They don't pay tax or NI on the value of the salary they obtain in the form of childcare vouchers. A lot of parents I meet didn't know about either of these.