Typically the drag cars were scheduled pre-Winternationals, but late rule changes and/or approval could mess that up as well as having them done & tested in time.
For example, a '64 Hemi RO sedan was tested at Lions in late winter with AFBs while the Maxies were current, and then revised with Holleys. If memory serves, some '65s were ready for Pomona, and some delayed until the 2nd NHRA event @ Beeline. The '65 program was kind of broad: the sedans, the 4 A/FX HT cars, and the 10/15-inch AWB cars. Things happened on a monthly and even weekly basis.
Seems Chrysler & Ford both had that kind of schedule: I don't recall the T-bolt intro date, but the '68 CJ 428 Mustangs debuted publicly at the Winternationals.