You suggest a course of activity—described in no more than 25 words—to twelve or fewer creatures you can see within range that can hear and understand you. The suggestion must sound achievable and not involve anything that would obviously deal damage to any of the targets or their allies. For example, you could say, “Walk to the village down that road, and help the villagers there harvest crops until sunset.” Or you could say, “Now is not the time for violence. Drop your weapons, and dance! Stop in an hour.”
Each target must succeed on a Wisdom saving throw or have the Charmed condition for the duration or until you or your allies deal damage to the target. Each Charmed target pursues the suggestion to the best of its ability. The suggested activity can continue for the entire duration, but if the suggested activity can be completed in a shorter time, the spell ends for a target upon completing it.
Using a Higher-Level Spell Slot. The duration is longer with a spell slot of level 7 (10 days), 8 (30 days), or 9 (366 days).
* - (a snake’s tongue)
It's a shame that Warlock lost this spell, but overall it's still still incredibly good.
I've got good news for you: Warlocks actually still have this spell because 5e still exists to be played.
Does the suggested effect apply immediately, or does each creature wait for its turn to comply? I'm asking to know if its possible for a different creature to dispel the charm effect before the affected creature's turn.
The effect is applied immediately. Whether the targets can actually do anything about it immediately depends on what the suggested course of action is.
For instance, if the suggestion is "drop your weapons", then the targets will have to try to do that on their next turns, because you can't drop things when it's not your turn.
On the other hand, if the suggestion is "don't attack me", then they have to immediately refrain from attacking you, even if they would have an opportunity to attack you before their turn (e.g. you provoke an opportunity attack).
In any case, it is possible for someone else to dispel the effect at any point after the spell is cast.