I don't think buying a girl now and waiting would be much of a problem.
You just never know about females though. My oldest "Peep" does fine in my sorority. She is the top dog though. Pretty much no one bothers her. Every
once and a while, one will sneek up on her but for the most part she is
"IT" I bought Peep on Easter weekend. I started my sorority June 14th. Now that some of my girls are getting bigger they have started challenging the others. As of last night I have had to take two out to let there fins heal some. They were looking pretty bad. I rearranged the tank and put the other 4 back in. So far so good. Figure I will let my other 2 girls heal for a bit, then rearrange the tank again and see how it goes.
You just never know with females.

They can turn on each other at the drop of a hat.

Some just get along with everything.

The ones that started out being a bit shy are now coming out of there shell and pecking to the top. One of my smallest "Chirp" is now huge and has made her way from the very bottom to the second in command. But, my most timid fish in the beginning "Tweet" has started really going after anything that moves!

Guess my point in this lengthy, wordy, going on and on, is ......you just never know what is going to happen with the girls.

They may get along just fine for the rest of there lives, or....they may not get along from the beginning, or....they may get along at the start then not get along...or who knows?