The maximum group name length is tied to the maximum username length setting (settings > users > max username length). The default value of 20 can be set on the web interface to an arbitrary value such as 99, but above 60 characters the error message “too long” appears when creating a group.
set max username length (settings > users > max username length) to 99
try to create a new group (users > groups > new group) with a name with more than 60 chars