Charging time for AA Batteries

Hi,
(A) I have used 6 AA (total 7.2 V) batteries in a kid’s toy (Contest F1 Racing Car; 1/10th Scale, No.: 6643 ). Pls find battery details below:
1. Sony rechargeable batteries / Cycle Energy Multi-Use Premium Rechargeable Battery (Ni-MH AA, Pre-charged 2500 mAh; Model no.: NH-AA-B2GN).
2. All 6 batteries are connected by Kyosho / Tamiya Connectors.
I would like to know:-
1. How long I will have to charge all these 6 batteries with:
(a) The charger / adapter provided with that toy (Model: YX-3515A8, Input: AC 220V 50/60 Hz, Output: DC 7.2V 250 mA). Batteries (6) provided with this charger (L J BATTERY RA07d AA 500mAh 7.2V; these 6 cells are not so good quality).
(b) The charger / adapter I made with the help of a technician for the better performance / result (Model: DJ-E060500, Input: AC 230V 50/60 Hz, Output: DC 6V 500 mA).
(B) I have used 4 AA (total 4.8 V) batteries in a kid’s toy (Jeep, Military Corps Special, Cross Country, 1:16 Scale, No.: 360A). Pls find battery details below:
1. Sony rechargeable batteries / Cycle Energy Multi-Use Premium Rechargeable Battery (Ni-MH AA, Pre-charged 2100 mAh; Model no.: NH-AA-B2KN).
2. All 4 batteries are connected by 2 pin JST Connectors or Male Connector w / Wire for 1 / 18 Battery C22630 (may be / I am confused); pls find attachment for the pic of that 2 pin Connector in Adapter side or pls check this link https://www.integy.com/st_prod.html?p_prodid=6566#.U6Ya2bEmETg .
I would like to know:-
1. How long I had to / will have to charge all these 4 batteries with:
(a) The charger / adapter provided with that toy (Model: XD-048250, Input: AC 220-240V 50/60 Hz, Output: DC 4.8V 250 mA). Batteries (4) provided with this charger (Model unknown; these 4 cells are not so good quality and already out of order).
(b) The charger / adapter I made with the help of a technician for the better performance / result (Model: PH-0450500 UP, Input: AC 220V 50 Hz, Output: DC 4.5V 500 mA).
(C) What is the charging time for rechargeable AA batteries (separate 02 / 03 pcs) when it is used several times earlier not the first time.

(D) Does pre-charged Sony Ni-MH AA batteries need to charge before use !

Thanks

1. The normal charging time for Ni-MH batteries is around 10 to 12 hours. Fast charging time is around 6 hours.
2. Ideal time required for charging (Hours) = (capacity in mAh)/(charging current in mA)
3. However due to several factors the time obtained above must be multiplied by a factor of approximately 1.1 to 1.2
4. With 250mA charger 2500mAh battery will require (2500/250)*1.1 = 11 hours.
5. With 500mA charger time would be 5.5 hours

1 Battery capacity is 2000 mAh and for 6 batteries (6X2000 mAh ) 12000 mAh

I would like to know these charging time is for a single battery or for all 6 batteries connected in a series circuit !

I mean:
If a charger has 500 mA then the charging time for 6 batteries (total 7.2V): 2000 / 500 = 4 Hrs or 12000 / 500 = 40 hrs ??

What about a charger of 7.5V and 1000 mA for charging these 6 batteries! Will it be: 2000 / 1000 = 2 Hrs or 12000 / 1000 = 12 Hrs !!

Pls explain.