I think that 5 hours of continous playing are not realistic. If you do backyard shuttling or play against shitty opponents, than you get kudos for withstanding such boring matches.
If I play at my level and slightly above 2-3 hours is realistic to play serious without too much fatigue. IMO badminton is no marathon and one game is just 3 sets max. One MD or XD match can be 25-35 minutes. I play normally 4-6 matches. If you aren't tired enough after 4-6 matches, your opponents must be **** or you are not giving all you can put into the match. Just my 2 cents.