That's one place where the SAFE is better than a convertible note - a note will have to have a specific term for maturity, usually 18 or 12 months, but a SAFE can just sit there outstanding indefinitely until an event causes it to convert.

This could get tricky. I imagine, at some point when you feel the round is closing, you'd want to set some terms/valuation and ensure that the biggest investor (or most/all of the investors) feel good about that.