First, if your Kegel muscles are very weak, you may not feel like you are doing it at all.
Second, if your pelvis is messed up, it is the release of the Kegel that is more significant that the contraction.
Third, for me I have figured out that a Kegel is 1. tightening my anus, 2. have my clitoris "nod down", and 3. closing up the vaginal entrance. Don't flex your butt and don't use your transverse abdominus.
If you are trying to release your pelvic floor, don't strain to hold it. Just initiate the Kegel for 1-3 seconds and then release and try for "non-doing" relaxation (i.e. don't try to consciously "enlarge" your anus). This may take a lot longer than the Kegel - 30 seconds? 1 1/2 minutes? 4 minutes?
If you are trying to strengthen your pelvic floor, then hold the Kegel just until you start to lose control and your Kegel gets shaky.
Here is where the biofeedback machine really helps as it measures your muscle contraction and relaxation through electric impulses.