wow I been keeping respectable-strong. with between 48-70 minutes...
in generally,to have a good game shape, you must ensure that none of your players do not play more than 96 minutes .
Do I need more minutes to get the whole team up to proficient??
this also depend on your players... some players have a proficient game shape just playing 48 minutes,others need more minutes-50-80 and others can have a proficient game shape just playing 35-45 minutes. you need to find what kind of players you got in you team.
Is it possible to get a 12 man roster all to proficient, or you saying we should just keep the starts/starters at around that?
it is possible, if you train game shape :)