How long can I leave 2 Male Bettas flare at each other (from different tanks)?

[DiiQue]

I have two tanks that are side by side right now and the two guys have a flaring contest whenever I remove the dividing cover. I figure letting them see each other for a bit would help entertain both of them and they can share war stories. How long can I have them do this without causing undue stress? Right now I just leave the cover off for 5-10mins and then add the cover back on. Their tanks are a good 4 or 5 inches apart, so every once and a while, one goes to the other side of their tank and relaxes.

[DragonFish]

Lol, share war stories....I love it. xD
I think 5-10 minutes sounds about good. I wouldn't go over 15 minutes max, but thats based more on personal preference and worry....I'd start to get nervous around 15 minutes that I'm stressing them out too much myself.