In June 2017 on a week day, our cruise ship docked at terminal one and many of us took either the 25 or 27 bus that stopped nearby. We did not see a #26 as mentioned in our guidebook. The 25 dropped us in Norreport, a central location near metro and within easy walk to main parts of town. On our return we waited over 75 miutes for the 25 bus which never showed. Other bus drivers said it was not their company or the bus sometimes did not run as scheduled despite the posted schedule. So four of us who had just met at the bus stop and were on the cruise, took the same taxi back to the ship. We noted that the name of our ship, Zuiderdam, was posted on a billboard enroute to the port. So do not depend on the buses to return you to the port.
When going to the cruise port, we caught the bus in front of The Tivoli--across the street from the city hall.
We'd already scouted out the bus number and made sure the bus stop had that number on the sign--ahead of time. No problems.
Bus 25 is a temporary service during the cruise season. It only runs when there are ships in port and the last bus leaves Nørreport one hour before the last ship sails. You can read more here http://dinoffentligetransport.dk/KoereplanerPdf/25-0025-300417.pdf
So no you can't depend on bus nr 25 to return you to the port if you haven't read the schedule and try to depart after the last bus has left. But you could have taken the train from Nørreport to Østerport st or Nordhavn st and changed to bus 27. All this travel information and more is available at www.rejseplanen.dk.
I believe the bus numbers are 25 & 27 to get to the port. We had no problems getting into the city from the cruise port.
On the way back to the ship, it was another story.
There was construction happening there on June 22 when we were there with NCL.
The final re-boarding for the day out in Copenhagen was set for 4:30 pm. We were at a bus stop (Osterport) at around 3:30 pm. The electronic bus sign stated the bus was coming, but nothing came waited for almost 30 minutes. Another couple was there and we ended up spliting the bill on a taxi. Was about $10 for the two of us. Made it on time to board.