Charging time of recharge-able battery (TR 18650 8000mAh 3.7V)
How many hours should I charge this recharge-able battery (TR 18650 8000mAh 3.7V) ?



Unfortunately the question is moot, as those batteries are lying about their capacity.

With the current state of technology, it is impossible to have an 18650 cell with 8000 mAh capacity; now, in 2019, about 3600 mAh is the maximum (some testing of claimed 3600 mAh batteries suggests that their real-world capacity is a little lower). Therefore any calculations you make, based on their claimed 8000 mAh fake capacity, will be wrong.

For further details, do an internet search for the terms: ultrafire fake capacity

I remember seeing testing of some similar deliberately-misdescribed batteries, where the actual capacities found varied significantly and could be only a few hundreds of mAh (and of an unknown quality and therefore unknown safety too).

Examples of testing other Ultrafire batteries with fake capacities, can be found here:

UltraFire TR18650 5000mAh (Blue) 2014 - lygte-info.dk
UltraFire TR18650 5000mAh (Blue) 2018 - lygte-info.dk
With any Li-ion / Li-Po batteries, the safest way to charge them is with a dedicated charger, which implements the correct CC/CV charge profile, detection of low initial voltage, suitable charge termination etc., following the limits on the battery datasheet. This has been covered in previous questions.


  Let's say the charger converts 5V input source to 3.7V internally.


You don't charge a battery labeled as 3.7 V, using a 3.7 V voltage source. Please research Li-ion charging, as I mentioned above.