Yes it is true that if u surf on MTNL dial up in the night the pulse rate of the telephone call doubles.
1 .Thats is if during the day you are paying Re.1 for 3 minutes then from 10:30pm to 6:30 am you pay Re. 1 for 6 minutes.This is for the local call.
2. I am not quite sure what are their charges for the ISP services . I think it was 10 ps / pulse but then they revised it to 7-8 something. I am not sure.
Check out the 2nd point .
The daytime charges are anything above Rs 20 because Rs 20 is the amount you have to pay for using the telephone ( Call charges) + ISP charges I think it should come up to Rs 25. Not more.This is just an approximation .
Regards