You lose around 4 exercise bows for every period of 12h you dont train offline. Thats 100 tc or a little more than 1kk gold.
You can easily test for yourself with fresh characters from dawnport. If you take a level 8 paladin to the training statues and leave him training for 24h (12h training and then 12h resting), he will advance from distance 10 to almost 46.
And then if you take another level 8 paladin and start training with exercise bows:
- First one will advance his distance to 32
- Second one will advance his distance to 39
- Third one will advance his distance to 42
- Fourth one will advance his distance to 45 with 64% progress.
In another words 12h of offline training equals 2000 exercise weapons charges for distance skill. This number can go down if you take in consideration players target dummies, but then you have to remember that offline training also increases your shielding.