It will depend on local childcare providers - some will be able to offer flexible places, others will not. Some providers may offer a pay-as-you-go service whereby you book individual days/hours as and when you need them but that can be risky as what if they are full and can't help you?
Start by contacting local providers and asking them about what they offer. Have a good idea of what the shift patterns are likely to be - how far shifts are planned in advance.
Your local Family Information Service can provide lists of local childminders and nurseries. Family Information Service is usually part of your local or county council.
When asking about costs, calculate your total cost over a year. Some providers will charge for times when they are closed, others will not. Fee structures vary so do not assume, always ask for details about fees and situations when a fee is payable. For example if you child is ill, do you still pay? If the provider is closed do you still pay? What about Bank Holidays - are they open, closed and do you still pay or not?
Consider ease of getting to the provider. Keep things as simple as you can I would suggest, so that you are not rushing to get there, or to get back in time to pick up.
Consider if you want your child cared for with other children of a similar age, or in a mixed age group. Childminders will have a mixed age range of children - a nursery may have a mixed group or they may have babies all grouped together. Babies can enjoy being with other babies but they can equally enjoy seeing older children. Older children may not be around all the time - they go to pre-school, school - so being at a childminders is more like being part of a big family. That means baby does go on the school run, so they get out and about but you could also say they get dragged around. Whereas at nursery they can be in one room the vast majority of the time - though some nurseries I have temped in have taken babies out for push in the pram and when there have been just a few have mixed them in with older children.
Look around several different providers - look at a couple of nurseries, a couple of childminders.
You may find the Mumsnet Childminders/Nannies board a useful place to find out more about childminders and issues that crop up, plus the Mumsnet Nurseries board for info about nurseries and issues that crop up.