There is a recommended diary that is posting incorrect information regarding whether participants can leave after signing in. The correct answer to this question is YES. I am a precinct chair and I received this memo last night.
If, after the convention has been called to order and participants have signed in, any participant who wishes to leave may do so, and their sign in WILL count toward the delegate allocation for each candidate.
This is important because many people cannot stay for various reasons and would be discouraged from participating. Here is the link to the official document on the Texas Democratic Party Website.
Every one should stay if they possibly can but do not be discouraged from attending if you cannot stay for the whole convention. PLEASE go to the TDP website if you have any question about the precinct conventions.