my job , a night shift , starts at 2 pm
i am permitted to take time for only one of 2 tefilot, either micha or maariv ,
should i prefer mincha since arvit is “reshut” ?
Yes, you should take time off for mincha before taking off for maariv, because it is reshut. However It seems that it is still possible for you to daven maariv after your shift finishes, unless you are working from 2pm until the next morning. Even if you can’t find a minyan then, you can still daven without a minyan.