This shouldn't really be a public discussion. Its a private arrangement/act between u and ur fiance, and therfore she should be the only person u should discuss this with. However, i would suggest to just go with the flow, and let the atmosphere rule ur first night 2gether.
If you and youre Fiance can talk about everything...then why not tell her not to expect a lot the first time...and that's just natural for first timers....I'm sure she'll understand....
Or....before u get in bed....release urself in the washroom...that should give you a few extra moments.... :0) ...