Whereabouts are you? Are you coming into spring, or going into autumn?

SoCa

I'd be inclined to leave it until the weather warms and the palms have had a chance to settle in.

People ask this kind of question all the time, but what they should be asking is when they should be using a topdress Nitrogen fertilizer to help the palm grow.

First there are different types of fertilizer and people don't even think about this. I like to use different fertilizers to make my plants do what I want them to do at different times of the year, when applicable.

So, if you put triple super phosphate in the hole at the time of planting, it will make the roots grow twice as fast, and since it is only 0-46-0, there is no Nitrogen to burn roots. This makes newly planted plants, in general establish much faster. Every plant I pot up gets this. Then, most fertilizers that are time release and are made to be incorporated in the soil can also be put in the hole at the time of planting. I love Nutricote for palms as anyway. I use 360 day Nutricote 18-6-8.

So, if I were to do this, I would put TSP in the hole and also the Nutricote. TSP lasts a month and it takes 2 months before the Nutricote reaches maximum release, so by the time the TSP stops working, the Nutricote is kicking in. You could even top dress with TSP after the first month to help grow the roots even more and make it establish even faster.