nicnic if you're serious about a loft conversion I would get cracking now.
You need to think about possible structural work, electrics, heating, decorating, flooring. None of these jobs takes weeks in of themselves, but making sure the contractors are available when you need them is the fun part. The main delay will be caused by availability of contractors (should you be using them) and building regs.
Most loft conversions do require building regs approval, since it's a change of use, and often new structures such as windows/doorways are involved. Also the change of use means there will be more stringent requirements on things like fire exits. Building regs are not the same scary thing as planning permission. It's not a decision in advance, it is a check during and upon completion of the work, that the the work has been done to a minimum standard. If they aren't happy with what they see, you will have to do it again! Most reputable builders will submit building regs on your behalf, and if they don't understand them DON'T USE THEM!
It is entirely possible to do all the work yourself, apply directly to the council with building regs and get it all passed off, but you need to be sure what you're doing is correct. And the regs get updated regularly, so check them even if you think you know.
I have done a lot of building work, can you tell?