Here's one example: vip_rental.txt
Usage: (can be used in an item script or NPC script)
{ callfunc "F_VIPstart", <ticks>; }ticks = how long their VIP will last, in seconds
1 day = 86400
7 days = 604800
14 days = 1209600
etc.
Example item script:55555,VIP_7day,VIP Membership (7 days),2,2,,10,,,,,0xFFFFFFFF,7,2,,,,,,{ callfunc "F_VIPstart", 604800; },{},{}