How early should I book a mobile disco?
It has be considered that the better DJ's tend to get booked well in advance and the closer it gets to your event the less choice you will have.
Then again, if you are prepared to chance it, the best prices can often be had on a late booking.
Probably don't chance it on public holidays such as Christmas or August Bank holiday, almost without doubt any DJ worth his salt will be booked close the day.
Is it the kind of event where you want to gamble on getting a DJ at all?