How much time do I have to commit?

As much or as little as you like. The more you do, the more Time Credits you can spend on getting things done for yourself.

What about tax and benefits?

Time Credits earned participating in Time Bank activity will not affect your social security benefits or tax liability

How does it work in practice?

Exchanges are made with the help of a Time Broker who links people up and keeps a record of transactions made. The Time Broker also keeps a directory of services offered and requests received. Data and records are, of course, secure and confidential.