The lack of consistency and accuracy with the model forecasts this weekend is almost enough to force me into finding a new hobby.
The 2am runs of the models has the GFS bringing rain by early afternoon. The GFS-based LAMPS short range has rain by mid morning here. The NAM still holds off most of the rain until late afternoon and this evening. The NAM-based HRRR shows rain moving into PHL about 3 PM.
The further north you are from PHL, the earlier the rain starts.
So there you have it. The HRRR did well yesterday so about 3 PM looks like a good bet here in PHL. Areas to our north, in Bucks county, upper Montgomery counties and Trenton, already have rain or will have it starting in the morning. Areas as close as Blue Bell might have rain starting later this morning, according to the LAMPS.