well... to be honest, there are people who do not read the forums every day, there are people who do NOT stalk the Dev Tracker for every bit of information.
So no, IN THE GAME... or in the launcher there was NO mention of any rewards beeing time limited.
I think they do a bad job at letting people know these things, it wasn't even on the Homepage as a news, just hidden somewhere in the Forum.
If you call thise "beeing clear" about something, then sorry but no, they can do a better job at giving these infos out to the Playerbase.
The information is put in the FAQ on the Featured Series webpage, which is available from the Launcher during each Series. Each time the Launcher has a link saying "time to play episode X" it links back to the Featured Series webpage. If people don't want to take the time to read the FAQ or learn about the Series limitations that's not Cryptic's fault. They're not going to put a quote on every episode ad in the Launcher saying "Remember the special reward only lasts a limited amount of time!" They've already said that in the information they're linking you to. Cryptic's provides the information. It's the player's responsibility to read it.