iPhone unavailable. Try again in 8 hours

If you know your Passcode, you'll need to wait the 8 hours. If you have forgotten your Passcode, there is no alternative but to erase your phone to get back in. It's unfortunate you don't have a backup, but the time to ensure no loss of data is BEFORE something goes wrong. No one can help you if you haven't been regularly backing up your phone.

If you have indeed forgotten your Passcode, the related article link at the top of this tells you how to erase your iPhone using your computer. You can however erase your iPhone without a computer, IF you know your Apple ID and Apple ID password by following the directions in this link --> If you see an iPhone or iPad unavailable message or Security Lockout screen – Apple Support (UK)

Either method you use, you're going to lose your data. This is an unfortunate lesson you'll be forced to learn. Once you rebuild your phone from scratch, use the tools Apple gives you and use iCloud Backup.