There are three different possible solutions in my comment, which one did you try?
Note that the first time LibreOffice opens it takes longer than subsequent times but 30-40 seconds is a long time unless you have LibreOffice installed on a spinning HDD hard drive instead of SSD. Or you have the LibreOffice portable app on a pen drive, that can take a long time too depending on pen drive and USB port.
To save time on slower devices you can click Tools > Options > LibreOffice > General and tick the box Load LibreOffice during system start-up.
Could it be a delay in accessing the file on a compressed drive/another drive/network location? Or maybe the anti-virus software is set to scan files before opening? Could it be a File manager issue, I find that Windows Explorer often takes 10 seconds or more to get itself together on first opening before it display anything and then changes location twice more over the next ten seconds.