I was finishing up a Hermetic Diagnois for a client today, and when I was talking to Tzadqiel of Jupiter about some of his financial issues, I was told that there was little that could be done to increase the Jupiterean forces in the client's sphere until he was out of Retrograde, which doesn't happen until December 25th. There were things he could do to improve the general well being of the client, but for this one specific plan the guy had in mind, there wasn't going to be any outpouring of new blessings until after Christmas.
I was also told that if the client would have done the Jupiter rites before the retrograde, there would have been more Tzadqiel could do now. It's like when you're building a house, there's a part of the work that has to be done when the weather is clear, but once you've got the frame built, you can cover it in plastic and keep on working on the plumbing and electric even before the roof is put on if necessary.
Now there have been other clients who needed Jupiter Work during a retrograde, and it was no problem. Maybe they had less specific aims in mind, or maybe they had laid enough of a foundation while he was Direct to be able to work with during the Retrograde. Or maybe this one client's natal chart leaves him personally susceptible to Retrograde Jupiter, or maybe the other clients' natal charts left them with the ability to receive Jupiter blessings no matter what the astrological weather was like. Chris Warnock or Austin Coppock would be able to decipher the details better than I can, I have no doubt. There are so many variables to take into account.
In general though, it seems like its a good idea to do the foundational building up Work with a specific planetary power while they're direct, and then maintenance Work when they're retrograde.
A panacea that would address all the variables regardless of their causes would be a regular regimen of working with the planetary powers. If you cycle through the seven planets on a regular basis, communing with their Intelligences, working with the powers of the sphere, you'll have a good momentum built up that will assist you when something unexpected pops up.