Set Launch Page for WordPress blog

Hello, wondering if anyone can help me with this.
I’ve got three main parts to my music blog, the main page (www.indiemusicfilter.com), the mobile site (in subdomain, https://www.mobile.indiemusicfilter.com) and a videos site (www.indiemusicfilter.tv).

I recently created a static ‘launch’ page to appear and show for 4 seconds when people are arriving at the main page (www.indiemusicfilter.com). The launch page is https://www.indiemusicfilter.com/launch.html, allows people a choice of which of the three sites they’d like to go to.

What I’m trying to figure out is how to set this page up so that it appears when people head to indiemusicfilter.com.
as well, I’d like it to only appear once while people are surfing the site, think the line of code in the launch page does that properly (<META http-equiv=”refresh” content=”5; URL=https://www.indiemusicfilter.com/index.php” >).

I recently tried editing my htaccess file with the line DirectoryIndex launch.html, but it created a loop in wordpress.

Hope I’m explaining myself well enough here, anyone got any ideas?