Help, my husband fertilized our Hollies with 10-10-10. They are yellowing and I am certain instead of the 10-10-10 they need Holly Tone. How soon may I apply Holly Tone?
Zone 6b

I don't think it necessarily was the 10-10-10 fertilizer that did it -- maybe it was how much he used? The maximum amount to use is no more than 1 Tbsp per foot of height.
As to when to apply Holly Tone, keep in mind you'd just be giving the tree more fertilizer (Holly Tone is 4-6-4). Check the package instructions to see if the manufacturer of the 10-10-10 gives recommendations for feeding trees/shrubs and work from there.

What about using Ironite?

Ironite is still a fertilizer -- albeit one with very low percentages of N-P-K (1-0-1). Best check with your husband and find out how much fertilizer he applied ... too much love will kill a holly shrub faster than too little.

I use Holly Tone, but not on my hostas. I don't think they require acid fertilizer. On my hostas, I use an organic fertilizer called Harmony 5-4-3. My mom has been using it for 4 years, and her hostas are HUGE!