Do it from the very beginning.
Membership fees are but one way to monetize an online community.
Two main strategies here:
- Allow members to join for free and encourage them to ‘upgrade’ to paid membership.
- Charge a one-off application fee just to get in.
I recommend strategy 2.
If you charge someone to join your community you weed out everyone but the most willing and the most enthusiastic.
No more tire-kickers.
You get an immediate cash contribution and you get a member who is far more motivated.
An added bonus:
You get to spend time managing and developing the community, not ‘encouraging’ members to upgrade.