how does that relate to the 200maH that the 9V block has?
It says the absolute maximum time is half an hour, in practice it is likely to be half this.
I am considering using several batteries in parallel
Don't do it, you will get all sorts of problems with the batteries cross charging each other, even with non rechargeable ones.
Those small 9V blocks are very poor at current, you are best off using some AA NiMh rechargeable ones.