Driver's license? Theory test?

I won't be of legal age for another eight months, and I can't take the theory test until three months before my 18th birthday. I've already completed two theory lessons and need another twelve. I don't want to stress myself out too much, so I'm wondering: Does it usually take a long time to get an appointment for the theory test? Or is it quick? Otherwise, I would just do everything during my holidays and then take the test straight away.