It seems to me that if they are naturally curious and enthusiastic about what they're learning, they will find some way to learn about it regardless of deadlines, policies, and frenetic environments.

Accordingly, keep some red meat around to toss their way whenever they appear to be hungry.

The alternative, telling them to stop wasting their time, causes more harm than good and probably will be ignored.

(speaking in general terms, not specifically about you or your workplace)

Cheers,
Matt