There is no real answer to it, some people have double xp, others play nothing but S&D, there's different game modes with  their own xp. There's too many variants to give an exact answer, one guy may take 12 hours, another could take forty hours, it really depends on how well you play, if you have double xp, what game modes you play in, how many different guns/perks/killlstreaks/equipment you use for their challenges. For me personally, I usually take 24 hours playing different game modes, when one game mode gets dull, or there's too many people camping hard I switch to another game mode. I find it a little faster to rank up if you play team defender with specialist on, just make sure your team has the flag and earn the specialist bonus, I've done that and for eight or so games I've had no less than 10,000xp, highest was just over 60,000xp. AS for tenth in only three hours,I would highly doubt it, even with all the HC and Community games you play.

I am what I would consider to be an average player. It takes me about 20-30 game play hours (7-10 days) to complete each prestige with no double xp.

Currently 283 hours played level 30 prestige 12 my average score per minute is right at 200 if that gives you an idea how long it takes to prestige.

Edit also good point about HC I have also heard the time played does not show correctly

there is no exact answer for sure. depending on the game mode, it can take anywhere from 12-40 hours. also depends on how well a person does in matches, how many challenges they complete...

and elite didn't keep track of hours played in hardcore or community playlists, so that could be a determining factor when you are wondering about whether or not a person got there legitimately.

Im currently sitting at level 60 Prestige 5. Ive played 124 hours in total. 94 hours spent on TDM. 10 hours on Domination. 9 hours on Kill Confirmed. 11 hours on Other game modes.

It takes me an average of 23 hours to prestige. I have used 2 prestige tokens on doublexp during my 124 hours of play.