Shorter buffs sure, but not worse as they will be full potency.
The lineup otherwise just feels very awkward, you sing at minute 0, recast HM in 10, rest 5 mins later, Hm 5 mins later again, then everything 10 mins later again and repeat. Very stop/starty when you can just fire everything up for 10-11 mins and be free for other responsibilities in the mean time.
OK here are your scenarios, starting with present (ignoring dummies):
SV 4 songs with Gjallarhorn, Hmarch with Marsyas
2.5 minutes later, Nitro 4 songs with Gjalla, Hmarch with Marsyas
13.5~ minutes of SV, then you go on to do regular songs with no SV.
With MC:
SV 4 songs with Gjallarhorn, Hmarch with Marsyas
2.5 minutes later, do 4 songs with MC, HMarch with nitro Marsyas
10 minutes later, do non-nitro HMarch
~4.5 minutes later, do regular songs with no SV
17~ minutes of SV (except Hmarch which is still ~13.5)
The only difference is that your SV is 3.5~4 minutes longer, has 1 less +song, and you have to cast 1 more Honor March. That's it.