as you can see, You can not take a deduction for your time/svc. That would be like deducting it twice. If you invoiced for your time/svc , were paid, and then gave the money back, you can deduct that donation. But, if you received no money, you can not deduct the value of your services. Since there was no price tag on the services, there is nothing to deduct.
Say there was a doctor worked for 6 months, and charged regular fees. Then, the doctor worked 6 months at a clinic, for free. If the doctor deducted the time donated, then the doctor would have no taxable income. This is not correct. The doctor would have to report the income from the first 6 months, but the second 6months is not deductible. However, the doctor would be able to deduct expenses, like travel to and from the free clinic, etc.