Once a form is finalized by the IRS, it has to be coded into the special language the software uses and has to be thoroughly tested for calculations and e-filing acceptability. The IRS then has to approve it for e-file. It always takes a little longer for a form to become available for e-file in a software program. The dates are subject to change due to all that needs to be done.
Here is an article you can reference that will tell you particular forms availability.