Well I’m not an ISV and haven’t built desktop software except at school a long time ago and those were pretty much just learning exercises.
But I can give you my opinion as a user. I see absolutely nothing wrong with a piece of software taking ~3 or 4 seconds to start. (I’m guessing the time you measured represents the time to load on your computer but that will depend on what kind of computer the software will run on)
As a comparison, the desktop software I personally use the most are Netbeans, Photoshop, Illustrator, Chrome, Firefox, Spotify, foobar2k, keepass, Steam, and a few other here and there.Most of these take over 3 seconds to cold start and I’m fine with it. Once it starts, it’s running for a long time and as long as the app is responsive and useful once it’s running I don’t think there’s any issues with it.
Now, If you had a webapp that took 3 seconds to load each page, then I’d have some harsh criticism for you.
Still, if there’s any way to make your app significantly faster, then go ahead and do that. Or maybe add a loading image at startup. But I think your time would be better spent getting customers, adding features or starting your next app.