Re: AM stations broadcasting “Critical hours” in Alaska
I can't speak to the specifics of your question, but generally speaking there are some unique traits of Alaskan radio that play into what you're asking.
There are relatively few stations statewide in Alaska. There just isn't the need for them. Alaska, the largest state in the US by far, has less than 700,000 people, the vast majority living in three major cities (Anchorage, Fairbanks, Juneau) and the Mat-Su Valley (Wasilla, Palin's hometown). Much smaller population centers include Kenai, Sitka and Ketchikan, Bethel, and coastal villages like Kotzebue and Nome. Between all these cities and villages is a lot of. . .nothing. Small Native villages with maybe a few hundred people dot the landscape, and once you leave the road system there are only about 10 places with more than 1000 people (Anch, Fairbanks and Juneau are the only cities statewide with more than 10,000 people). So the need for 50k stations isn't that great to start with. Most villages have stations built specifically for that village or region of the state. Empty land, high mountain ranges, and huge bodies of water separate these villages and prevent signals from reaching all parts of the state. (Again, this is generally speaking - I'm in Anchorage and I often pick up stations from Nome, McGrath, Glennallen and Fairbanks.) My point is that in Alaska, for the most part, there is no need to boost a signal to reach an area beyond the local footprint.
Another thing to consider, w/r/t critical hours, is that there are relatively few stations outside the state close enough to be affected by local signals. The few stations I pick up regularly outside of AK are from San Francisco (KGO 810 and KCTC 1050), Vancouver (CKNW 980 and CKST 1040), Seattle (KOMO 1000), and a few others. None are affected by AK local stations. The big 50k watters here in Anchorage (KENI 650 and KFQD 750) have no nearby signal competition down south (the small CISL 650 near Vancouver BC being the closest one, which actually increased power after moving to that freq, and KXL 750 in Portland OR, a 50k that seems to operate interference-free). Alaska is just too far away for it's stations to really affect anyone else. That's not to say it can't happen - I'd be interested to know what AK stations are picked up in, say, Washington, Oregon and California, and I've heard several cases of Anchorage signals being heard in Honolulu.
Hope this helps answer your question.