Can my old iPhone 6 that has 16GB do a time-lapse all day?

Can my old iPhone 6 that has 16GB do a time-lapse all day?

That depends on whether the iPhone 6's battery can last all day being in photo mode, the resolution of the captured images (HDR or non-HDR?) and the number of images captured. And we assume the 16 GB is available to use… Not an iPhone that was built with 16 GB has a bunch of apps and other photos or music so there's only 1 GB available for this time lapse project…

For example, if 1 image (JPEG) is 3 MB, and "all day" = 24 hours

24 hours x 60 minutes in an hour = 1,440 minutes

If an image is captured once each minute, then 3MB x 1,440 = 4,320 MB or a little over 4 GB.

If an image is captured every 6 seconds, then there won't be enough room.

So… You provide some details and maybe we can provide a better guess.