I think like many venture axioms, founders get bad advice here out of good solid rules
The 18-24 month rule is a good one — until it isn’t.
The real answer is Until The Traction Where You Know Someone Will Write You Another, Much Larger Check.
I know this is subjective, but pay attention. Listen to what the expectations are. Ask your current investors. Talk to VCs you know, but that can’t invest now.
Find out what it will take.
And stretch your cash to get there. However long it takes.