I don't think the site has published any time control stats for variants but if they have the message it is very likely the case.
Though, people looking for variants probably also watch the seek graph and pick them up from there too, so you may not notice problems with getting games with other time controls.
I get this message when I create Crazyhouse and King of the Hill variant requests:
"Get matched more quickly by choosing 3 | 0 for variants."
Is that statistically true? I feel like I get about even numbers. Was it true before (perhaps because people just wanted to try the variants) and now is more evenly divided?
Thanks!