Google Checkout doesn't allow 2 day durations. You need to use durations within Googles limitations. Limitations as follows.
1 Year,
1 Month,
2 Months (Every Two Months),
3 Months (Quarterly),
12 Months (1 Year),
1 Week,
1 Day,
7 Days (1 Week),
15 Days (Semi Monthly),
30 Days (1 Month),
90 Days (Quarterly),
365 Days (1 Year)
Any durations outside the above ranges are forced to the closest allowed duration.