I would allow 45 minutes from the time you are walking out the exit at DHS to walking through the tapstiles at AK. While the bus ride itself won't be much more than 15 minutes, Disney recommends allowing at least 45 minutes per leg of a trip because of wait time for the bus, walking to and from bus stops, bag check and getting through the tapstile.
If you are heading to AK for a dining reservation, FP+ res, or start of one of the shows I would allow an additional 30 minutes, especially if it's something like a dining res at Yak & Yeti which is at the far end of the park from the entrance or one of the shows where the audience is let in well before the start time of the show.