yes it is highly likely that the offers will be made before the GS results are out and there will be some pressure to get you to accept before March 1st. However - hang in there, they can't make you decide:
I posted this last year:
edit: found this on beechwood's website:
As the Kent 11+ selection tests will now take place in September, some independent schools have moved their 11+ entrance tests forward to the Autumn Term, and will no doubt be offering places to successful applicants soon afterwards. Whenever testing takes place, however, the regulations of the Independent Schools Council clearly state that there should be no deadline for acceptance of places before the first week of March 2011.
At Beechwood, we have therefore decided to keep our Entrance Day in January, because it fits in better with our school year. We believe that this will still give parents plenty of time to come to a decision about their child's secondary education.