During jhana do you eliminate all hindrance at once? Are you suppose to try and eliminate all the hindrances at once or slowly elimate them one by one? If this is the case are you suppose to eliminate them slowly in one meditation session or slowly rid them until they are all gone During multiple sessions?
Jhanas are attained by suppressing the five hindrances via concentrating on  objects like the breath, or a kasina object, etc. But if one contemplates on anicca, dukkha, anatta, one automatically starts reducing, not just suppressing the hindrances. In this latter type of jhana, it is attained via using Nibbana as the arammana (thought object). This is not “an object” per say but a contemplation on anicca, dukkha, anatta. In both these cases – the ‘Anariya’ or ‘Ariya’ Jhanas (or the mundane or the supra mundane), the hindrances are suppressed or reduced over time, and not all at once. For this one needs to focus the mind forcefully onto one thought object (nimitta), not letting those five hindrances come to surface.

This second kind of contemplation leads one to attain the Sotapanna (Stream Entrant) stage of the Noble Eightfold Path. Then these five hindrances are reduced to a level that is sufficient to attain the first jhana with the jhana factors of savitakka, savicara, piti, sukha, ekaggata fairly easily. When the five hindrances are kept at bay, and one feels the serenity of a mind unpolluted by the hindrances, this is called samatha meditation – that attains the ‘calming of the mind.’

The two hindrances of kamachanda and vyapada were reduced to kamaraga and patigha levels at the Sotapanna stage. Kamaraga and patigha are reduced further at the Sakadagami stage, are removed at the Anagami stage. Thus an Anagami is left with rupa raga and arupa raga, and thus one has only attachment for rupa loka and arupa loka.

On the other hand, the hindrance of thina middha is easily overcome by savitakka, i.e., when the mind is focused on Nibbana (anicca, dukkha, anatta). Thus any sleepiness or lethargic feeling cannot survive and one feels energetic.  A Sotapanna is at the entry level of comprehending anicca, dukkha, anatta, and the understanding gets progressively better as one moves to higher stages. 

The hindrance of Uddacca also decreases by stages. Here one should note that without cultivating jhanas, an Arahant automatically removes all five hindrances, but this also happen in stages and once it happens it is permanent. Ariya jhanas are permanent in nature compared to Anariya jhanas. Thus a Sotapanna will be able to easily get to the first Ariya jhana in any of the future lives, because some of the five hindrances have been permanently reduced, and vicikicca permanently removed.

It is Vitakka that inhibits the hindrance of sloth and torpor (thina middha). Then at the time when mental happiness (Piti) arises in the mind, this jhanic factor of piti suppresses the hindrance of ill will (vyapada). Then the body becomes light due to physical happiness (sukha), and it is this jhanic factor that counters the hindrance of restlessness and worry (uddhacca kukkucca). The moment that one gets to one-pointed-ness (ekgaggata) in meditation, this one-pointed-ness temporarily inhibits sensual desire (kamachanda).