As soon as possible. The amount of time it takes to interview and process a visa varies greatly. Information on wait and processing times can be found here: https://travel.state.gov/content/visas/en/general/wait-times.html/
If you are applying for an O or P visa, you must first have your petition approved by USCIS (see here: https://travel.state.gov/content/visas/en/employment/temporary.html). Petition approval may take as long as 180 days.
Please let SXSW know how you intend to enter the United States (whether using the VWP or a visa) by February 4, 2019.
For more information about obtaining a visa or estimated timeframes, a list of attorneys and agencies is provided in the Additional Resources FAQ.