The original idea came from Jeff Schwartz in is updated version of the game "Project Phoenix". He used to be around here but I have not seen him in a while.
I have a link to PDF rules on my gaming site.
http://games.juhlin.com/files/ProjectPhoenix.zip
His interpretation is a little different than mine, but as it is science fiction you have a lot of leeway in how you use it.
I have the bubbles run time inside at about 2000 times slower than the outside world.
The generation occurs from the inside of the bubble. The fixed radius is established via regulated power flow.
EM transmission on certain frequencies can pass through the field, but interpretation of such data would require specialized equipment to compress or expand the signal due to the time distortion.
Bolt Holes could receive communication, and even communicate out, but with a significant delay. The compression effect of the field barrier generally limited the communications to very simple letter combinations similar to the ELF system.
The field was to be brought down if
1) The System receives its "Wake Up" signal.
2) The System has run for 5 years external time and the crew turn it off (assuming a "Stay Asleep" message was not received)
3) The power generation system can no longer support generation.
The system as tested would shut down instantly, but the longest test was 2.5 years (external time) and above ground. Under those conditions the the problem of temporal inertia was barely noticed. Short runs underground also did not see the problem. However when the combined effect of larger fields, long run time, and additional mass were all combined the effect was disastrous.
After the expected wakeup, there could be sporadic communications, limited by the 3 letter code system. The radio reception/compression system could also fail after a decade or so leaving them without the ability to "hear" anything while they wait for the bubble to collapse.
I used to think that caches would not have time fields (rendering them nearly useless after 150 years) but the discussion of medicines and their expiration has let me to rethink that part of the equation.