Hi,
Thanks for using our plugins. I can help out here.
We do not have a feature to do as you describe.
If you think that is something you would like as a feature I encourage you to visit our User Voice Page and either upvote an existing request or make a new request there.
http://tribe.uservoice.com/
It could be possible with a customization, but as that involves the admin not sure how feasible it is. Create a Javascript function to check a field and limit the characters would be the best way to go. We are unfortunately, limited in supporting customizations, but I can try to answer a question or two about it.
Cheers