@adam
No hard and fast reason, the thought is the longer the prize is redeemable the more non-listeners will somehow discover and game the system.
System gaming vs. Bots & farms:
Any amount of time 24/48/96 will attract bots/farms if the LTBcoins per magic word is lucrative enough. Just a thought:
I could easily create a script that logs in to 100,1000,.... accounts and makes a post to a particular page and leave the magic word, and so could a lot of other people (unless you had a capcha box in which case I'd have to get more creative). What if the Magic word didn't give any tokens, but instead gave a multiplier of a users weekly contribution. So instead of giving 1000LTB/episode give 0LTB (or a very minimal amount like 10LTB) and multiply their weekly participation earnings by 1.05. If my weekly participation were 5000LTB that week I'd get 1.05*5000LTB = 5250LTB. Maybe a 5% bump is to high or low, and you could have a scale of how each episode listened to affects the % bump (1 episode = 4%, 2 = 7%, 3+ = 9% etc...)
This way, WHEN I start my evil LTB magic word bot scheme I won't actually be taking much if anything away from the community.
I'd worry less about single users seeing the magic word on a forum post and entering it in. They are probably somewhat active anyway and this keeps them engaged, even if it is only minimally engaged. A guy taking a few tokens by entering the magic word is a potential user and part of the community. Bots/Farms on the other hand will only take away from the community. At the very least add a capcha box to the magic word entry, but even that isn't a 100% solution. Would it be worth someones time to get 1,000x the LTBcoin offered for entering the magic word each week?
PS
I'd also prefer the magic word/listening time to be extended to 96+.
Also, is there a feature that would let me create 1000 user accounts with a file upload, or do I need to have a script for that as well? :) just kidding.