Well, that is what some people are recommending to new sellers.
It’s possible that some buyers may filter to only see buyers who are online. But I think, it is more important to have a good gig title, description, gallery, tags first. If your copy does not convert it does not matter how long you are online.
I have been a buyer since 2012 and I’ve never filtered my search to only show online sellers. It’s not like I expect the seller to deliver the order in a couple of minutes. I just sent a few messages and waited a few hours and see how they are responding. That is more important to me than their being online.
As a new seller myself, all of my orders were made while I was asleep, mostly probably because of the timezone.
That’s my experience anyway. How about you?