As far as a double TR goes,

You need 4,300,000 xp  (approx).

If you powerlevel on the high XP per min quests as much as possible and keep an xp pot on you can easily hit 1k per minute. 

That means it takes 4,300 minutes to double TR.  That is 72 hours (approximately).

That would be possible in 3 days of straight play.  14 hours per day to get it done in 5 days.  11 days would mean about 6 hours per day of play time.  You can do that and still have a job and/or a social life.

3 months to double tr would be 40 minutes per day working on the toon or about an hour and a half a day if you were only earning 500 xp per min instead of 1k per minute.

It's not that hard.  Even non-powergamers can get it done in less than a month.