I think it is bad design in those tournaments:
OR they start at the specified time,
OR they start when there are 6 people inside.
I can not enter and say let's go to the bathroom or get some drink, because they start immeditey after they are full regardless of the announced time.
Well it never happened to me a round robin tournament is not full before the start time, Iwould be curious about what happens.
And finally, if you write 6 people min 5, where there are 5 why should it "waiting for 1 player"? too confusing.
I understand if you should write "waiting for 6 players or the announced time, whichever happens first" sounds ugly, but actually it is the best description.