First of all, I've found some reference that state in a very well designed study that the improvement in mood occur regardless of the time of the day.
( Take in consideration that in this particular study the exercise protocol was only lasting 20 minutes ).
You have to consider that some times the improvement in the mood is even not related to measurable parameters of exercise ( it doesn't depend on the nature of the exercise itself ).
Experimental procedures to assess exercise impact on the mood should be very precise because there are a lot of studies out there that are not so precise.
In conclusion, to answer your question: yes is it possible that your mood improves in such short time. But there will not be ONLY strictly scientific clues to that; mood is not a scientific concept in close sense, and there will always be other variables that influence it other than hormones and neurotransmitters.
The second reference however, if you can get it in full paper, is a comprehensive meta-analysis on all mood studies.
You will not see in the tables the duration of the exercise protocol, aswell as the type and the intensity ( actually more influent variables ).