Yep.
You get 300 mins to last you for 30 days. That means 10 minutes per day. O2 will give you 300 minutes every month on the 1st (the first installment being the first of April).
However, they have given you 3 days allowance (10 * 3) for the 3 days before this just so you can use your phone before the 1st of April 
