I bought and installed 5.5.7 at the end of February 2021. Worked no problem and I created a couple of simple timelapse videos. Today I went to load the program and it hangs at the welcome screen (just tells me it is loading directories). The only way I can close it is to reboot the machine.

Hoping to improve matters I uninstalled 5.5.7 and downloaded and installed 5.5.8. Reinstalled latest Adobe DNG Convertor. However it will still not get past the welcome screen.

Do you maybe have connected any external drive or mounted a network drive that makes the loading of the folder tree stall?
On Windows: add the folder C:\program files\LRTimelapse 5 to the whitelist of your virus scanner.

If this doesn't help, check out the log file after this happens (you'll find it in Documents/LRTimelapse).

At the beginning there will be a line like:
Loading settings from C:\Users\gwegner\AppData\Roaming\LRTimelapse\user.props

This tells you where the settings file is. Force close LRTimelapse and delete that file.
On Mac: open finder, chose "Go to folder" from menu and paste the folder from above, without the "user.props". Then delete the file.
On Windows: paste the folder (also without the user.props) into the explorer bar at the top. Then delete the file.

Then try launching again.

If the problems persist, send me the log file to support(at)lrtimelapse.com

I have a NAS and several PC on a network. Going through your steps above has been successful and I am up and running again. Thanks.