Unless you have a specific early market “niche” or requirement for harvest management your main reason for using dormancy breakers is to compress bloom. Early application of dormancy breakers spreads bloom rather than compress bloom. This is bad news for chemical thinning, crop management, particularly at harvest and disease control. If your objective is early harvest lifting rates may improve bloom compaction so overcome some of the lack of bloom compression from an early dormancy application.
Micro-climate also influences dormancy breaker response. In general terms inland valleys cut off from the sea breeze are two weeks earlier for application than coastal sites. Cultivars and tree age differ too.
Mature trees respond to early application of dormancy breakers better than young trees. Again, there is about two weeks difference here too. Some cultivars, Pink Lady® group for instance, do not need dormancy breakers here. It is also doubtful for Scifresh unless the block has a history spread bloom problems.
Try to benchmark your dormancy breaker application against an earlier dormancy breaking deciduous tree. This will tell you if the spring is running early or late so you can adjust timing accordingly. For bloom compression in mature Royal Gala types optimum timing here is around mid-August for bloom compression.
Russet prone varieties e.g. Scired, require later dormancy breaker application, as well as a dormancy breaker that will bring leaf buds out with blossom buds.