Every creature on that planet has exactly the same 24 hours a day - no more, no less.

So what this "I do not have time for that" can be broken into the following:

1. "You waste your time on something I would never spend a minute". This one means "I do not want to spend my time for this since I do not want to do it". It is fine, let it go.
2. "You are doing things I am dreaming of, but I am stuck with my day to day routine so no time left for this". Aha! This one is good. That means "I do want to do it, but I cannot set right priorities, and I cannot manage my energy and time to do it".

If the answer is 2 then get this work item into your pipeline - this is how I manage mine (My Pipeline Is My Inbox).

Then ask yourself "how bad I want it?" - the "bad" scale should help to estimate how much time to spend on it.

Once the time is set there are no excuses anymore.

The other question would be  "how I prioritize?".

Jason shares his very nice and simple rules here - Priorities for Tough Decisions.

Enjoy