A friend on twitter was due to attend an eye test at Specsavers and tweeted that they requested the contact lenses in at least 4 hours before and given that his appointment was 9:15am that meant getting up at 5.
I replied to say surely he could take the lenses into Specsavers the night before, however it turns out they meant you are to be wearing your lenses from 4 hours before.
Makes much more sense.