2mbps at night is limited period offer till Jan 2013 I think.
I don't see it mentioned anywhere, But I don't think MTNL downgrades speed's after upgrading it, they mostly upgrade speed every 6 months or a year.
Hehe, Maybe after 6 months I hope they change my day speed from 1.344 Mbps to 1.792 Mbps & evening + night to 2 Mbps. I think that's the maximum they can do soon.
Unless they planning to introduce , 6Mbps, 8Mbps & 12Mbps on their higher plans on DSL in future. 🙂