MacBook Air does not turn on, only shows battery icon

Eight hours should have been more than enough. If you can, substitute a different USB-C cable. The cable has to specifically support charging, and some don't.

The one included with your Mac should certainly be the correct one, but there was a short time (perhaps a year or two ago) during which Apple shipped cables that didn't meet their requirements. So if you need yours evaluated by an Apple Store or AASP, bring all three devices — the Mac, the power adapter, and the cable.

It needs time to charge.

If you have reason to believe sufficient time has elapsed and your Mac's battery is still not charging, refer to If your USB-C power adapter isn't charging your Mac - Apple Support and If your Mac battery status is "Not Charging" - Apple Support.