Variant Channels with no duration

[Driver 325 yards]

Example:

Quote:

Freedom: Heal—Creatures gain a channel bonus on Escape Artist checks, CMB checks to escape a grapple, and saving throws against becoming entangled, paralyzed, or slowed. Harm—Creatures are slowed (as slow) until the end of your next turn.

So the heal variant has no duration. The duration for variants are typically 1 minute, end of your next turn, and next roll.

If it is silent, how long does the effect last?

[Oxylepy]

It's either permanent because the effect is not stated with a duration, or it lasts until the end of your next turn based on the Harm effect.

Unless they errata it, I'd just say stick with your best judgement.