My sMerits were scarce all the time, if I have 5 sMerit to spend then I will try your challenge next time. 
I just checked my data, and indeed nobody ever Merited 5 posts within the same second.However, Foxpup pulled it off with 6 posts:
Quote
Merit sent by Foxpup (Trust list) from January 24, 2018 until July 30, 2021 (source)
3700. Tue Nov 19 15:53:16 2019: 6 (10510) to tobyyola (history) for Re: 10th anniversary art contest
3699. Tue Nov 19 15:53:16 2019: 6 (10504) to sedactoo+04 (history) for Re: 10th anniversary art contest
3698. Tue Nov 19 15:53:16 2019: 10 (10498) to Welsh (Trust list) (history) for Re: 10th anniversary art contest
3697. Tue Nov 19 15:53:16 2019: 9 (10488) to Basorexia (Trust list) (history) for Re: 10th anniversary art contest
3696. Tue Nov 19 15:53:16 2019: 4 (10479) to yarelydiaz (Trust list) (history) for Re: 10th anniversary art contest
3695. Tue Nov 19 15:53:16 2019: 4 (10475) to Eduarop (Trust list) (history) for Re: 10th anniversary art contest
3700. Tue Nov 19 15:53:16 2019: 6 (10510) to tobyyola (history) for Re: 10th anniversary art contest
3699. Tue Nov 19 15:53:16 2019: 6 (10504) to sedactoo+04 (history) for Re: 10th anniversary art contest
3698. Tue Nov 19 15:53:16 2019: 10 (10498) to Welsh (Trust list) (history) for Re: 10th anniversary art contest
3697. Tue Nov 19 15:53:16 2019: 9 (10488) to Basorexia (Trust list) (history) for Re: 10th anniversary art contest
3696. Tue Nov 19 15:53:16 2019: 4 (10479) to yarelydiaz (Trust list) (history) for Re: 10th anniversary art contest
3695. Tue Nov 19 15:53:16 2019: 4 (10475) to Eduarop (Trust list) (history) for Re: 10th anniversary art contest
(I'm not counting theymos' Admin tricks)