Can you post a picture or give some description?

there are a lot of mirabilis out there this year and this behaves like this.
google it and see if it is a match. unless you post a photo it will be difficult.

welcome to GoY :o)

Moonflower, some Evening Primrose, Datura, even some older varieties of Rose Moss (Portulaca grandiflora) might be worth looking up, too.

Morning Glory only blooms early in the day and mesembryanthemum close when the sun isn't shining on them.

There's also the wildflower that looks a bit like a dandelion on a long thin stem, popular name is "Jack goes to bed at noon" or "Goats beard". Pics of both on Google..

I'm intrigued to know what it is now.