You're not going to be able to eyeball GL3 and see a difference.

GL3 resets every 3 attacks. 3 attacks will not accumulate to a 1.0 second delta between the macro case and non-macro case, unless you are lagging at a horribad epic fail level.

To observe the difference, you need to use a longer sequence of attacks. One simple test is:

1. Get GL3.
2. Pop IR.
3. Immediately begin attacking. Sidenote: for best results, don't mash the button(s) and instead pretend you're being lazy in normal farm content, which is a normal use-case.
4. Count the # of attacks you successfully execute until IR is available again (60s of consecutive attacks).

The expected loss in # of attacks using the macro should be in the range of ~2 attacks.

That said, this level of testing shouldn't be necessary because it's pretty obvious when you press the button.

Sidenote: for best results, also pay attention to which attacks are actually executed. If you press the macro rapidly, you WILL eventually use Bootshine/DK out of sequence (e.g. when you should be using Snap Punch).

Edit: Kevee's method also works to demonstrate the specific issue and takes less time ... lol.