Use the Registry. Write an expiration date to the Registry the first time the .dll is called. Everytime it's called:
Code:
check Registry to find expiration date
If not found then
write date to registry (today + 30 days)
exit
End if
If found then
Read date from Registry
compare with today's date
Exit if today > Expiration date.
End if
Use the VB SaveSetting, GetSetting functions.
Use DateDiff() function to compare dates.