If he had the luxury of several days of preparation before the arrival, he wouldn't be pressed for time at the arrival, by any measure.
The story isn't clear on exactly what Spock had "little time" for, since the damage to Romulus was already done. Saving the rest of the galaxy from the wavefront? A bit unlikely, since the speed of the wave would still be finite and the galaxy is big. Saving his own life? Quite possible, as apparently Spock's ship was incapable of outrunning even the Narada in those particular circumstances. Collapsing the supernova before the very mechanism of collapse slipped from his hands? Quite possible again, as the creation of a tiny little black hole always sounded like a dubious way to contain a gigantic galaxy-swallowing supernova.
In either of the latter two cases, an interval of days between the loss of Romulus and whatever action Spock took would appear quite implausible.
Timo Saloniemi