Just like the medicine they are, all pesticides have unwanted side affects- usually, at the very least, killing some beneficials. The idea that the darkened buds bloom sooner is a side affect that probably went unobserved for decades. All springs are iffy at most sites. As a general rule, least possible harm comes from least possible intervention to achieve desired results when negotiating with Momma Dearest.

Dandy, glad I saw this and can save you from ken, lol. Crape myrtles benefit greatly by horticultural oil applied during the dormant season. Most (not all) species of aphids overwinter as eggs on the above ground parts of woody plants. There is a particular aphid that infests ONLY crape myrtles, and it just happens to be one of those egg layers, lucky for us. Insect eggs, just like all others, are gas permeable. The oil will smother the eggs very effectively, making a big dent in the numbers of aphids we have to deal with in the spring. Dormant oil applications break the cycle. For dormant season purposes, I'd recommend a refined petroleum product such as Volke Oil, which has been around for generations. But, you can also use any one of the commercial products that are so readily available. Read labels at the garden center to make sure that you don't purchase something with a bunch of unwanted chemicals. Read and follow the directions carefully, as always. It can be applied any time during the dormant season, three times over the course of the season with the last one just before the buds open in late spring. For the Crapemyrtle Aphid, be sure to spray the dormant buds and stem axils. As far as the rest of your garden, I wouldn't spray oils unnecessarily. Save it for those plants with known aphid or scale problems, when it can be very useful. Remember, Crapemyrtle Aphids are a big issue for crapes only. Plus, not all varieties of crapemyrtles are susceptible. It would be well worth your time and money to buy cultivars that that have been bred for resistance to such pesky problems like aphids and powdery mildew. Here is a link that might be useful: Click me

I think with the oils you don't want to apply them within 24 hours of freezing temps, not 100% sure on that. If your buds are already swollen it may be getting a little late to get disease control, particularly Fireblight. As the buds open they become susceptible to the spores washing into the tissue within them. Copper works well to nail the spore population before it has a chance to invade susceptible tissues.

Dormant oil IS horticultural oil. It is only referred to as "dormant" when that is the season in which it is used. Dormant oils used to be heavier, petroleum based products but broader applications and better refining processes now include so-called dormant oils with all other horticultural oils (many of which are still petroleum based but some also plant based). Even the very lightweight oils (best used in summer or during the growing season) can cause reactions with some plants. Many conifer types are included in this grouping of sensitive plants but not pines. "Dormant oil: An oil used on woody plants during the dormant season. This term originally referred to heavier weight, less well-refined oils that were unsafe to use on plants after they broke dormancy. However, these older oils have been replaced with more refined, light-weight oils that have potential application to plant foliage. Dormant oil now refers to the time of application rather than to any characteristic type of oil. Horticultural oils: An oil used to control a pest on plants. Summer oil: An oil used on plants when foliage is present (also called foliar oils). As with dormant oil, the term now refers to the time an application is made rather than to the properties of the oil."