Now a days the problems due to fog strats by enf of November or may be on the onset of December, so Nov first or second week shall be perfectly fine...Hmm..as far as catching the return train is considered, I guess a buffer of 2 and half hour would be just ok....but I would suggest you not to take that risk as on such a long journey you never know what may happen and 12259 may reach late for some unforeseen reason, and you may miss your return train...