You can file your federal tax return as soon as you have all the relevant information you'll need to complete it. Your employer has until January 31, 2018 to send out W-2s for prior year earnings, and most 1099 forms must also be sent to contractors by that date.
The processing of your return, however, will be determined by the IRS whenever they dictate. For instance, the IRS announced that the 2018 tax season opened on January 29th, thus the IRS began accepting tax returns on that exact date. Anything submitted before this date will be sitting in the queue until then, so your refund wouldn't be received any earlier.