Mike Kich:
Daniel makes it sound like a minute of solid concentration should be producing shockwaves, and I'm sitting there for half an hour and nothing's happening sensation-wise other than my one-pointedness getting better.
From
MCTB:
Tune into the illusory smoothness of things by purposefully and calmly working with illusions of solidity or fluidity. There is a certain “into it” quality which helps, sort of like really getting into a slow groove when playing an instrument, having sex, playing a sport, or just sinking into a well-deserved and warm bubble bath. Being in a silent and safe place is very helpful, as is giving yourself permission to relax, put the cares of the world behind you, and enjoy.
If you are using the breath as an object, you might try purposefully visualizing it as sweet, smooth waves or circles that are peaceful and welcome. Try breathing as if you were in a garden of fragrant roses and you wish to experience the fullness of their fragrance. Perhaps these tips will help illustrate the kind of non-resistant and peaceful presence that can help one attain these states. Tune into sensations in and around the primary object that feel good. Harbor no guilt, anxiety or fear related to the depths of pleasure, ease and well-being. The spiritual life need not be some sort of relentless, austere grind, particularly when doing concentration practices.
As concentration improves, it is as though the mind “sees” the first jhana and grabs on to it. Having an idea of what you are looking for, i.e. something enjoyable and steady, can be helpful for this. It has the five primary factors of applied and sustained effort or attention, rapture, happiness and concentration. Thus, it is great fun, feels good, but takes consistent effort to sustain.
I.e., cultivate metta. It's not the concentration alone which leads to rapture, it's resting the attention on pleasant sensations.
Mike Kich:
So my question is, how long does this "bringing up" of stuff usually last, or how long has it lasted in your experience?
About 11 years and counting, in my case.

It varies a lot depending on the nature of the conditioning and the quality of practice. Are you worried it's going to get in the way of school?