Yes you can freeze egg tarts if you want too and they will last for up to 2 weeks in the freezer.
However if you're gonna eat or serve the egg tarts within the next day then you can simply leave the egg tarts out at room temperature and they will be just fine.
Or you can refrigerate the egg tarts and then allow them to warm up at room temperature.
Egg tarts can be kept out at room temperature overnight.
While it's best to refrigerate egg tarts when you're keeping then longer than a day you can safely leave egg tarts out at room temperature overnight.
Egg tarts can safely be kept out at room temperature for up to 2 days before they go bad.
If you plan to keep the egg tarts longer than a few days then you need to refrigerate them and then when read to serve or eat the egg tarts just allow them to set out at room temperature for awhile.
Then the egg tarts will slowly warm up and be ready to eat or serve.
I have left egg tarts out at room temperature for 2 days without any issue.
So leaving the egg tarts out at room temperature overnight is perfectly fine.