Interface or file to find information about associated Device

I want to find the association time of the associated device connected to my OpenWRT installed router. Is there any possible way?

Yes, via the System Log.

iw dev wlan0 station dump

Thanks @vgaetera I had already used this command but I want to find the API that this command is using.

The API is at the driver level. iw is one user-space tool that uses it. ubus is another.

Edit: See also