Foresight, Barkskin and Mage Armor are examples of spells which require consent in order to function.
Could you revoke this consent at a later time of your own choosing in order to end the spell early?
No - and often the spellcaster can't dismiss it either
In 5e there are no rules-as-written regarding the target of spell (beneficial or otherwise) ending it early.
However, in the case of a spell that requires active concentration (such as Barkskin), it can be dismissed by the caster as a free action:
PHB, page 203:
If a spell must be maintained with concentration, that fact appears in its Duration entry, and the spell specifies how long you can concentrate on it. You can end concentration at any time (no action required).
Therefore in combat (assuming the DM allows it), the recipient of a concentration-based spell might be able to call out a short command to the caster and have them drop the spell - all without using an action. The DM might even rule that this can be done outside of either the caster's or the recipient's turns.
Spells that don't use concentration, however (like Foresight), cannot be dismissed early, even by the spellcaster, unless otherwise stated. From the article The Rules of Spellcasting on the Wizards website:
CAN A SPELLCASTER DISMISS A SPELL AFTER CASTING IT?
You can’t normally dismiss a spell that you cast unless (a) its description says you can or (b) it requires concentration and you decide to end your concentration on it. Otherwise, a spell’s magic is unleashed on the environment, and if you want to end it, you need to cast dispel magic on it.
Given that even the caster cannot end a spell like this early, it could well be ruled that the recipient cannot either.
By RAW, consent is needed only for the activation of the spell. It is not mentioned that this consent must persist. Therefore, the spell would last independently from the target's will. If there are conditions other than concentration and duration that affect the duration of a spell, they are always mentioned.