Overstaying period after refusal

Hello
My husband recently got refusal on ILR LR due to gap, we are going for appeal but wanted to make sure one thing.
I have searched alot but couldnt get my answer
His tier 4 visa was due to expire on 7th march 2011,he applied for tier 4 extension on 2nd march 2011 visa was refused on 27th march 2011 because they could deduct a fee from the bank account although there was enough money, he reapplied on 18th april 2011, visa was granted on 19th may 2011
Did he become overstayer after 7th march? Or 27th march? As far as i know there should be a grace period of 28days after refusal,

Please if anyone can answer this, it would be a great help
Thank you