Depends on how much luggage you have. You know the lingo, you know the country, so you could go to La Rotonda and take Javilla to POP...at 6 in the morning and a guagua from there to Sos?a...
I will check out their scheds for you and send you a PM or post it here...
HB
You do know that you can get good breakfasts over at the Supermercado Central, right? Just past the underpass? So you could arrive there, have breakfast and wait until Metro was ready to take you....OR you could "go Dominican" over at the Javilla station and get there a couple of hours earlier, I would guess...