Can i put my airpods in case while sleeping at night?

Hello,

Yes you can. When the AirPods are done charging, they no longer charge. They don't overcharge either.

From Apple's Website:

Get longer battery life

Your AirPods charge in the case and are ready for you to use as soon as you open the lid.

• To keep your AirPods charged, put them in the case when you're not using them.
• When you charge your AirPods with charging case, you'll get the best, fastest results by using an iPhone or iPad USB charger or plugging into your Mac.
• Repeatedly opening and closing the charging case can reduce the battery charge of the case.

From:

Charge your AirPods with charging case and learn about battery life - Apple Support