When using dispel magic to remove slow, when do the effects of slow end?

Question

I was curious about how someone using dispel magic to dispel slow during their turn would play out, since slow actively affects their turn.

The description of slow is:

You alter time around up to six creatures of your choice in a 40-foot cube within range. Each target must succeed on a Wisdom saving throw or be affected by this spell for the duration.

An affected target’s speed is halved, it takes a −2 penalty to AC and Dexterity saving throws, and it can’t use reactions. On its turn, it can use either an action or a bonus action, not both. Regardless of the creature’s abilities or magic items, it can’t make more than one melee or ranged attack during its turn.

If the creature attempts to cast a spell with a casting time of 1 action, roll a d20. On an 11 or higher, the spell doesn’t take effect until the creature’s next turn, and the creature must use its action on that turn to complete the spell. If it can’t, the spell is wasted.

A creature affected by this spell makes another Wisdom saving throw at the end of its turn. On a successful save, the effect ends for it.

So if a PC is slowed and successfully casts dispel magic on themselves this round (as in, they rolled under 11), do they immediately have all the effects of slow reversed (i.e. normal movement speed if they didn't move yet, a bonus action, normal AC if they provoke an attack of opportunity on their turn, ect), or are the effects of slow still active until the end of their turn?

Answer 1

Assuming the PC has successfully rolled below an 11 on the d20 to cast a spell, the spell takes their action on this turn. If it successfully dispels the spell, all effects of the spell are also removed.

An affected target's speed is halved,

This ends as soon as slow is dispelled. Since movement says you can move up to your speed, you are no longer impinged by this effect and any movement you might have left using your full speed can be used.

it takes a -2 penalty to AC and Dexterity saving throws.

This ends as soon as the spell effect ends.

it can't use reactions.

This ends as soon as the spell effect ends. Note that it doesn't say the PC doesn't have reactions, just that they can't be used while under the effect.

On its turn, it can use either an action or a bonus action, not both.

The PC has used an action on its turn to cast dispel magic. Assuming the spell is successful and it dispels slow, and the PC has a bonus action to make, the PC can now take that bonus action.

If they didn't roll below 11 then they are still affected by the slow until their next turn when everything stated above applies. In between these turns they are still casting the Dispel Magic which requires concentration: if that concentration is broken before their action on the next turn the Dispel Magic is lost and they remain slowed.