You could probably go from 1-50 in half an hour to an hour of running between leve NPCs handing stuff in if very rich and lucky enough for your worlds marketplace to have the HQ stock to buy and fulfill the best EXP rewarding leves one after another in quick succession, also having to take into account having enough leve allowance to get from 1-50. What is more realistic however is probably a week or few weeks for your average person putting in an average amount of time doing a mix of grinding crafting and doing some leves while not being very rich or lucky on the markets in order to hit 50 on one DoH.