Denise: from my personal experience, dissolving with agenda is a more advanced practice. I spent quite a few sessions doing inner dissolving without an agenda to really familiarize with it. Dissolving with agenda releases a lot of material from the emotional and mental body and one needs a good foundation to handle it.
It is much easier to relax and let go on the out breath but if you set up a good metronome of breathing, over time with experience dissolving can be done at any time during the breathing cycle. I practiced for 30 years in the Taoist Dragon Gate system before studying Bruce’s system so there is no hurry. But then again maybe I’m just a slow learner.
How it feels is a very personal experience and is different for every practitioner. It would be cheating you to describe it as it is better to discover for your own personal experience of the process. Best of luck. Will.