Dante took a couple of days to prepare for the trip. The city in which the Duke of Summer lived was quite a distance away from there—if everything went fine and Dante spent 2–3 days there before returning, it would still take him 13 to 17 days, depending on the paths they chose and the weather.
The month of January had ended, and February had just started. Leaving aside the first half of March, when the harvest festival was held, the second half would mark the official time for raids by Barons, lasting till the end of April. After that, the Grove Keeper would invite everyone to his home city; the whole of April would be gone in that event.
That left the official raid time for Earls and Dukes for May and June. Meaning the earliest Dante could be back—with or without Sable—would be in late June or July. Five months.