Where the defendant pleads not guilty the average waiting time between an 'either way' offence (such as Section 20 GBH) being sent to the Crown Court by magistrates and the 'substantive' Crown Court hearing is around 22 weeks.
However there will be a 'plea and trial preparation hearing' well before that.
If the defendant pleads guilty at the plea and trial preparation hearing, the time between the case being sent to the Crown Court and the substantive hearing is reduced to an average of around 7 weeks.
(Those figures are based up research in 2011. I doubt that the times are any shorter nowadays but, with increasing workloads on the courts, they might now be somewhat longer).