Hello and welcome. All summary offences (offences which can only be dealt with at mag's court) have a 6 months time limitation on proceedings being commenced. It's the 'being commenced' bit which makes it a bit of a grey area. The general consensus is that if the summonses are applied for then proceedings are commenced. You could also be charged with an offence at any time up to the 4th, but that's a little unusual for road traffic offences.
Allow a few days past the 4th for postage etc and you should be OK.