"Donating time" is a deceptive phrase because it just sounds like you are paying out some currency other than money and that's it. "Donating time" encapsulates "building friendships, lifting up others, increasing love/unity in communities, gaining new perspectives" and more, unlike "donating money" which encapsulates none of them.
I'm paid salary. I'm of the opinion that it is usually the self-absorbed that think that after they leave the office they are still worth what their employer pays them.
Making it a requirement that your time donation be within your professional skillset is saying, "such work is beneath me". I'm not above ladling a bit of soup into a bowl or picking up the dog shit while at the animal shelter.
I'm not opposed to that if you're doing it for your own benefit. But you should be thinking of this as leisure time for yourself, rather than assuming that you're "donating time" for the sake of real social impact. There's picking up dog $#!+, and then there's actually impactful stuff.
So, please donate time by volunteering! But if you can't, money is also good of course.
Basically if you make a high tier engineer's salary, you could do more utilitarian good by hiring several people to work at a food bank on the weekends. Roadside trash pickup is an example of a problem in need of a systemic solution, so if you can reduce litter in the first place, or build a machine that cleans everything, you might be doing more good that way, even though it doesn't look or feel as "noble".
But others have pointed out that it is useful to donate your time if you are giving your skills, and not just effort.
[0] https://youth.gov/youth-topics/mentoring/benefits-mentoring-...
Everybody knows the most important parts of charity are who gets the credit and one's own personal growth.
I am saying that credit isn't the point. Also, I am not entirely clear on why you would require $15/hour to volunteer at a charity...but...good for you turning charity into a second source of income.
Btw, my point (I will spell it out) is that the problem is almost never money. Money is required to the extent that is required to pay other people...but, particularly for almost all local problems, the issue is not money but time. There is no reality in which people donate enough income to solve these problems but they could donate time, and that would be effective.
By all mean, volunteer at your local soup kitchen. It is a great thing to do! But the money is more helpful on an ongoing basis.