I wonder if some of the newer breeders know how easy it is to keep adult Monarchs in prime condition...just waiting for any event you need to send them to? As Grace does some wedding releases here in UK throughout the summer and because I am always busy on other butterfly things, I find it much easier to breed for her a lot of Monarchs at one time, emerging them and then just keeping them fresh until they are needed.
To do this....after emergence...I give them a day of flight with plenty of nectar plants (combined with plenty of water misting) at the end of the day when quiet, I then post them through a wedge shaped slot cut into a fairly large stryrofoam box..I put back the wedge (The post box hole!) By the way I seal the box lid opening with paper tape first. It doesn't matter if you have them emerging over several days..the process is the same... just add them to the box and follow the routine. I keep a separate fridge for this which holds the temperature at 42f to 45f. (Don't be tempted to go any lower than this!) Every week or so I give them a days flight and feeding, then again at the end of the day when they are quiet again I just post them back into the box and then back into the fridge...you can keep them for ages like this. They will have minimal damage as they are in fact the same as they were when they emerged. They just go into a suspended animation while cool.
I like to line the inside of the box with netting to give a good grip while they are cool
All this really does is mimic their overwintering habits where they spend several months roosting together in thoudands...so don't be too concerned about packing a lot of them in close together!