Can i get a tax advance loan if i'm self employed? I've done my taxes with TT for the past 4 years. If yes, When is the soonest to file it and receive it ?

The refund loan is not available until certain qualified users can file and their return is accepted by the IRS.  The IRS has not yet announced when they will begin accepting 2018 returns.  It is unlikely to be earlier than the end of January or even later with the current government shutdown complicating matters.  When offered, the loan is put on a pre-paid Visa.  More details will emerge as TurboTax refines the information about it in the next week or so.

And because you are self employed, it is quite likely the program may not be ready for several weeks after non-self-employed tax returns are ready.