Amit , if you are new to mumbai and boarding from cstm to boriwali through harbour line, at your time mentioned , other that saturday and sunday ( all working day) you will find peoples already capture the seat from masjid(return train) and before the local stops at platform peoples board the train like mad.
You will got the standing , but be sure seat avaibility is very rare, and please if you had luggages , than do little late in catching the local, or go to Churchgate and take past 9.30 trains only.Connectivity from churchgate to borivalli is regular.Please do not catch any virar train else you will not get a chance to alight.