If a single aircraft only does PHL-TLV and back day after day, you'd probably be right - not enough ground time for maintenance. However, I assume that they'd rotate the plane over the various 330 routes, so one plane would be enough. For example, fly PHL-TLV-PHL then PHL-LHR-PHL, PHL-CDG-PHL, etc.
Jim
Maybe they will use three aircraft for a two day cycle continuing the flights in a loop like TLV-PHL-LAX-PHL-TLV or something similar.