According to tibia-stats:
A knight with a melee skill of 10 and 100% to go...
In order to get a melee skill of 80 in game you will have to train:
9 day(s) 3 hour(s) 5 minute(s) 46 seconds
While being offline you will have to train:
18 day(s) 6 hour(s) 11 minute(s) 32 seconds
If you add to this time, the time needed to regenerate your training stamina it will take you around:
36 day(s) 12 hour(s) 23 minute(s) 4 seconds
So u need more or less 110 days to make all skills to level 80 in this time if u focus on only one i willl get 91-92 skill.
In order to get a melee skill of 91 in game you will have to train:
26 day(s) 1 hour(s) 37 minute(s) 20 seconds
While being offline you will have to train:
52 day(s) 3 hour(s) 14 minute(s) 40 seconds
If you add to this time, the time needed to regenerate your training stamina it will take you around:
104 day(s) 6 hour(s) 29 minute(s) 20 seconds