I've recently been changing a voicemail setup and was wondering if it is possible to reduce the number of groups I've used.

The scenario is during the day if an incoming call is not answered within 20 seconds transfer it to voicemail, at night transfer immediately without ringing any stations. The following does this:

RP1 is night, RP2 is day
Trunk ringing - RP1=502, RP2=501
Station groups - 501 members=201,202,... next=502, overflow=20 | 502 members=3502 (a virt SLI) next=519, overflow=1
Create subscriber - 502=Both
Key programming - MW502 key for access to mailbox

To not use an extra group I tried:
Trunk ringing - RP1=3502, RP2=501
Station groups - 501 members=201,202,... next=3502, overflow=20
Preset forward - 3502 port=519, no answer fwd=1
Create subscriber - 3502=Both
Key programming - MW3502 key for access to mailbox

Which works at night, but not during the day. I've also setting all or no answer forward for 3502 with no luck.

I know group ringing at a station doesn't get forwarded, but as group 501 overflows to a station it isn't quite the same. Any suggestions to what I've overlooked, or will this just not work?