When is the best time to return from Mat leave?
Only you can answer that. It has to be when it suits you and your family, or your finances may dictate.
Where would my child be able to go and at what age?
Nursery, childminder, nanny if can afford it. They all have different minimums, some will take children from 6 weeks old.
Where would i put my child for the day? I will probably be partially working from home or may request a change in my hours. but those two options would still leave me with at least 2-3 days in the office. Are they childminders? nurseries? day care?
There are lots of different options. My advice would be to contact 3 nurseries and 3 childminders. Find out about their services, what is covered, what they cost, get a feel for what you like and don't like.
This will give you a good idea of what you want for your child and how much its going to cost you. Depending on your income levels you should research either tax free child care or benefit contributions towards the costs.