Explosives! You all piqued my interest...
The company I used to work for, Desert Star Systems, uses explosives in their pop-up satellites tags. Here are a few clips from their YouTube page outlining the process...happy to answer questions that I can answer.
https://www.youtube.com/watch?v=nHRMatNDnXI This video shows how their system is armed. Something similar could be used for your short-term release. These tags rely on a time/data parameter to release; however, developing a remote release isn't that complicated either.
https://www.youtube.com/watch?v=Isg5N-P3TXU This video shows the PCB that is inside the o-ring sealed chamber. The ignitor paste (?) that is applied by QuickBurst is what ignites the powder (seen in the above video) causing an internal explosion, and the force of that separates the two sections of the tag (same could be done with the electronics package attached to a collar). (Note: biologists use something similar to release equipment from whales and seals).
I believe that Desert Star has sold just the release portion of their tags (with wire leads) before, but you'd have to reach out to them directly.
Also, you could reach out to QuickBurst as well. They, QuickBurst, has gone through all of the appropriate procedures with the Federal agencies to ensure their 'explosive kits' meet their requirements for flight. In other words, you can fly with these kits. I have, many times, along with all of their customers.
Just thought I'd share...and I like blowing stuff up :P