Admiration of strength
Tolerance of weakness
and a recognition of ambivalence

For the very first meet start with 0 time as if you will meet them immediately,
Then consider:

Distance

same country - Add 1 week
Medium - Add 1 month
around the world - Add 3 months

Familiarity / Gut instinct of trust etc.

High - Add 1 week
Medium - Add 1 month
Low - Add 3 months or add eternity

Relation goals / intentions

Sex - minus 1 week
Friends - no change
Relationship - add 1 month

Current rapport level

High - no change
medium - add 2 weeks
low - add 2 months

So as you can see if you are meeting someone in the same country for sex and you have a high level of
rapport already and a high instinct of trust for them, you can meet after only 1 more week of talking online

If you want a relationship with someone on the other side of the world, and you don't feel like you can trust them
and haven't built much rapport yet then you have to wait until you've reconsidered your sanity.

I made at least half of this up so take it with a grain of salt ^^