Should Buddhists give their time to helping others? I'm new to Buddhism. I was familiarizing myself with the "Four Seals" in  This Article. 

The article connects the first truth, that all compounded things are impermanent, to charity. He said that giving our things to others is a good way to practice coming to terms with the fact that all things don't last. 

I was wondering if time is included as one of those "things" that we should disconnect ourselves from and give to others? Is time a "compounded thing?"
To evaluate this question correctly, it is essential to look at the difference of Theravada and Mahayana, since answers given by people from these differing traditions are bound to be slightly different also. It appears to me, the four seals are a mahayanic equivalent to the (not-only) theravadic three marks of existence. Also the Theravada/Mahayana-difference is also highly relevant to the question of time being compounded.

Essentially this difference consists the ideal that people strive after, which is the Arahant in case of Theravada - someone who destroys all bondages and gains enlightenment for himself and the Bodhisattva in Mahayana - someone who strives to enlighten all beings before attaining Nirvana himself or herself. (I'm being very brief here.)

The interpretation you refer to, charity as the answer to impermanence of things sounds to me to be typically mahayanic or vajrayanic (Vajrayana developed out of Mahayana).

About time: this is one of the trickiest subjects of Buddhist thought. Thinking over the Buddha's denial of ultimate ontological status for compounded entities (like "the person"), Buddhist thinkers tried to find out, what in the end has this ultimate ontological status, things that are uncompounded - asaṃskṛta/asaṃkhata. One of the perished schools of Buddhism - the Sarvāstivāda was especially noted for the theory of uncompounded, sort of atomic entities called dharmas, time being also made out of minimal time-quantums that all exist simultaneously in the present (past and future as well).

Nāgārjuna is supposed to be the first, definitely the greatest early Mahayana-teacher and his teaching polemicizes precisely against this theory of uncompounded smallest entities, claiming, that they do not exist, that really everything, including Nirvāṇa, Pratītyasamutpāda and time is compounded. His teaching can also be read (thereby being truly mahayanic) as a rejection of self-centered hunger for enlightenment and thirst for Nirvāṇa.

Therefore, at least according to Mahayana the answer to your questions are yes, time IS compounded, we SHOULD disconnect ourselves from it, from clinging to it and we SHOULD freely spend it on others.

EDIT: replaced Hinayana by Theravada.