OP: would it make more sense setting shorter times which I can finish?
When one does not have Sampajañña, i.e., know there is a sensation and know it is impermanent one is accumulating Sankhara / Karma. 1
In daily activities, a novice generally does not have Sampajañña, therefore accumulates Sankhara.
When one is in proper meditation (not merely sitting on a cushion distracted) one does not accumulate sankhara and also dilutes the effects of past sankhara.
Also during a meditation session, there are times one remains distracted and it might take a while to settle into a serious meditation.
Therefore a meditation session should be sufficiently long to compensate for distraction during meditation and the lack of Sampajañña during daily activities. Short sessions may not give desired results. E.g.
- polishing brass takes some time to remove the oxidisation. If you do this for a short time then this will not restore the shine.
- to create fire one needs to rub 2 sticks until they catch fire. If you stop rubbing prematurely it does not light up.
OP: Is there such a thing as the momentum of accomplishment in meditation or even in virtuous activity in general? Or, is such a feeling of success a kind of attachment, and problematic?
If one tries to perceive the quality of a meditation session this leads to disappointment or satisfaction. This counters what meditation tries to achieve that is not to be averse or attached.
1
i. On seeing a form with the eye,
- one investigates the form that is the basis for mental joy,
- one investigates the form that is the basis of mental pain,
- one investigates the form that is the basis of equanimity.
ii. On hearing a sound with the ear,
- one investigates the sound that is the basis for mental joy,
- one investigates the sound that is the basis of mental pain,
- one investigates the sound that the basis of equanimity.
iii. On smelling a smell with the nose,
- one investigates the smell that is the basis for mental joy,
- one investigates the smell that is the basis of mental pain,
- one investigates the smell that is the basis of equanimity.
iv. On tasting a taste with the tongue,
- one investigates the taste that is the basis for mental joy,
- one investigates the taste that is the basis of mental pain,
- one investigates the taste that is the basis of equanimity.
v. On feeling a touch with the body,
- one investigates the touch that is the basis for mental joy,
- one investigates the touch that is the basis of mental pain,
- one investigates the touch that is the basis of equanimity.
vi. On cognizing a mind-object with the mind,
- one investigates the mind-object that the basis of mental joy,
- one investigates the mind-object that is the basis of mental pain,
- one investigates the mind-object that is the basis of equanimity.
Dhātu Vibhaṅga Sutta
- Know that the feels are impermanent so do not cling onto them
If he feels a pleasant feeling,
- he understands that it is impermanent;
- he understands that it is not to be clung to;
- he understands that there is no delight in it.
If he feels a painful feeling,
- he understands that it is impermanent;
- he understands that it is not to be clung to;
- he understands that there is no delight in it.
If he feels a neutral feeling,
- he understands that it is impermanent;
- he understands that it is not to be clung to;
- he understands that there is no delight in it.
If he feels a pleasant feeling, he feels it in a detached manner.
If he feels a painful feeling, he feels it in a detached manner.
If he feels a neutral feeling, he feels it in a detached manner.
Dhātu Vibhaṅga Sutta