maint. plan scheduling

Hi All ,

I have created a Strategy based maint. plan with monthly based strategy. I have defined 1 month=4 weeks.So when i m scheduling the maint. plan for 365 days , I m getiing 13 calls instead of 12 and in one of the month there r two maint. orders. Now the issue is the maint is done by external party on annual contract basis( they will do maint. 12 times in a year) . Now what to do to solve the issue?

regards