Does Teferi, Time Raveler's static ability prevent opponents from activating abilities at instant speed as well as casting spells?

Teferi, Time Raveler has a static ability that reads: 'Each opponent can cast spells and activate abilities only any time they could cast a sorcery.' This wording explicitly covers both spells and activated abilities, restricting opponents to sorcery speed for both.

Under CR 307.1, a sorcery can only be cast during your main phase when the stack is empty and you have priority. Teferi's restriction mirrors this: opponents cannot cast spells or activate abilities during your turn, during combat, or in response to other spells or abilities — they must wait for their own main phase with an empty stack.

Activated abilities are defined in CR 602.1 as abilities with a cost and an effect separated by a colon. Normally many activated abilities can be used at instant speed (CR 602.3a), but Teferi overrides this default for all opponents.

Note that this does not affect triggered abilities (CR 603.1) — those trigger and go on the stack regardless of Teferi. Also, mana abilities (CR 605.1) are generally exempt from timing restrictions, so opponents can still tap lands and other mana sources for mana even under Teferi's effect.

Example: Your opponent controls a Viridian Shaman and wants to activate a Basilisk Collar's equip ability during your attack step. Under Teferi's restriction, they cannot — they must wait until their own main phase when the stack is empty to activate that equip ability.