Benzyladenine and gibberellic acid in for formulation of GA4+7 and 6-BA has been shown to help mitigate damage from froist/freeze events. This material is sold under the tradenames Promalin and Perlan. The label covers only the bloom period. Unless in the bloom period, you should not use this material for frost rescue.
Since frost/freeze events are sporadic/unpredictable, there has been limited research related to use of Promalin for frost rescue. Following a series of frost events in 2012 during the bloom period
McArtney et al. (2014) demonstrated an increase in fruit set and yield in some cultivars when using Promalin. This was true with applications up to 5-6 days following the freeze event in this study. See data from that study below.