PilotPieces:
I believe GAPAN are quite particular about applicants fulfilling all the terms written on the application form - this ensures fairness for all. The way I interpret the application, as on page one, is that the Class 1 need only be valid on the 15th July 2009, i.e. the medical must be passed (and not revoked) any time in the year leading up to that date.
However, if you do not already have a Class 1, it would be rather difficult to fill out the Medical section on page three. If you're not willing to get a medical done immediately, perhaps you could delay sending off the form until nearer the closing date, when you have taken the Class 1 medical.
I'm almost certain that not getting a medical until after the application process is complete would not be permitted.
However, I'm sure the Guild office would be able to offer the definitive answer, just a phone call away.