The Core?!
It took almost the same amount of time for everyone to regroup than it did for them to actually finish marking their route. That's not to say that it took Celaine Maria, Elenei, and Mira each another 12 hours to make it back as that was only the case for Celaine.
Elenei had made it back to the meeting point in about half an hour. She would've made it back sooner, but she decided to keep her guard raised so she doesn't fall in some random trap. One mustn't forget that she reached the edge of the Formation in about 3 hours.
Even after making it back to her original position, she still had to wait almost 9 hours before the rest of her companions would even start making their way back.