Kind of a damned if they do, damned if they don't situation. They will certainly be able to call it early, but not sure any network wants to be the one to call it too long before polls close -- they can lose viewers and take flak from the losing side for doing it. Once one does they all follow pretty shortly, of course.

OTOH, if they all wait until West Coast polls close, there will be a few hours where the talking heads have to pretend that basic arithmetic doesn't exist. (Like S4P posters counting delegates.) In lieu of calling early, they might bring on one of Trump's surrogates for an early take on why they think the campaign was a complete disaster and "where they think the party needs to go from here" (or if we're really lucky, we'll get a delusional rant from said surrogate on how it's not over, Trump still has a chance guys because, look at how many electoral votes California has! I'm hoping for the delusional rants, meself.)

Control of the Senate (several close races there) could very well be what keeps us watching later. That and the Trump tears.