The Paypal enrollment plugin allows for setting "Default length of the enrolment period". AFAIK, in the English string tip there it looks as it must be expressed in seconds.

It appears to me that normal users would be happier to use it in days rather than seconds, as 30 days of enrollment period yileds 3600 * 24 * 30 = 2592000 which is not very meaningful and error prone to typos, not to mention the calculation needed to obtain and use it.