Timeframe of meditation's relaxing effect

If one just focuses on the feelings & sensations of the breathing, the feeling of air flowing in & out as you draw in & out, if one wants one can be thinking about the breathing if it helps to cut off distracting thinking, then one creates a bit of distance from compulsive thinking and it relaxes due to not be given attention, out of sight - out of mind.

First gross themes of thinking associated with sensuality, anger, worry, doubt, lust, thoughts about past & future and general disturbance cease before thinking is calmed altogether.

Breathing get's progressively stilled in the process in as far as the perception of breathing goes.

I guess it will take a while to start calming down, 3-15 minutes and 15-45+ minutes for breathing to become very subtle to the point where it's shallow & rare at which point one is quite secluded from unwholesome tendencies.

If one is doing walking meditation beforehand or is otherwise in a good mood one might not need any long time to attain deep samadhi as the mind is already secluded and saturated with joy & ease and at that point this is an opening and mind will direct itself based on it's inclination to a further settling in & enjoyment and one might then experience what people would consider mystical deep meditations of various kinds.

Sometimes focusing on breathing is not effective in cutting off distracting thinking and one might need to try other things to eliminate those such as directing the mind to a different theme associated with development of good qualities, examining the fault of the distracting thoughts & etc

When, indeed, bhikkhus, evil unskillful thoughts due to reflection on an adventitious object are eliminated, when they disappear, and the mind stands firm, settles down, becomes unified and concentrated just within (his subject of meditation), through his reflection on an object connected with skill, through his pondering on the disadvantages of unskillful thoughts, his endeavoring to be without attentiveness and reflection as regards those thoughts or through his restraining, subduing, and beating down of the evil mind by the good mind with clenched teeth and tongue pressing on the palate, that bhikkhu is called a master of the paths along which thoughts travel. The thought he wants to think, that, he thinks; the thought he does not want to think, that, he does not think. He has cut down craving, removed the fetter, rightly mastered pride, and made an end of suffering." https://www.accesstoinsight.org/tipitaka/mn/mn.020.soma.html

One should examine one's mind before sitting down and resolving on developing perception of breathing and see if it is suitable. Sometimes the theme of tranquility and concentration isn't appropriate as it won't rouse a sluggish mind.

Therefore one should also pay attention to one's themes of thought and not just ignore thinking altogether which is appropriate sometimes but ineffective otherwise.

In example if one is lazy & sluggish then you can sit for an hour and it will be close to taking a nap. One would here be better served spending 3-5 minutes on stirring up energy somehow and then doing anapanasati when one's energy is aroused. Same thing with lustful thoughts, the mind is simply too inflamed to focus on a bodily sensation and can be more effectively calmed by giving attention to the theme of eg unattractiveness, danger or another countering theme.

In terms of general quality of life effects, these should be immediate & proportional to the work you put in as the peace you set yourself up to experience by living disciplined & practicing mental hygiene should translate directly to more joy & happiness, if it doesn't then one wouldn't be doing it.