They need email but there is no 24 hour limit.
Rick
The email should be accessed and the signature completed as soon as possible. Let's say you're trying to sign someone up in Oct for an 11/1/14 start date using whatever election. If that application isn't signed until Nov, then the start date gets pushed to the next month (assuming the election is still valid).
I believe the use of a digital signature pad is tied to MAPA only -- the pad should eliminate the need for the email signature method and is its own digital signature method.