Originally Posted by Kotsubaki
His E animation takes longer than normal to cast, so it's a lot harder to land it against a running target. I noticed it the first few games I played with the skin.
malphite's ground slam uses the standard cast time of 0.25 seconds across all skins--you'll get the gameplay effect (damage + debuff) at the same time regardless of which skin you're using, and it's the same timing that was in effect before the patch.
something you might be noticing that's specific to this skin is that malphite doesn't immediately transition into his idle state after the spell effect triggers--he stays on one knee a bit longer and dramatically rips his fist back up from the ground (accompanied by a secondary powder effect around his fist when he 'shifts his weight' in preparation of rising again). this follow-up doesn't impact gameplay in anyway--you're able to move/cast at the same time as you would before--it's a subtle visual reward if you don't need to immediately move/cast after you slam the ground.
'flourishes' like that are things we like to add in when we get the chance.