Does Teferi, Time Raveler prevent opponents from activating abilities at instant speed?

Teferi, Time Raveler has a static ability that reads: 'Each opponent can cast spells only any time they could cast a sorcery.' Under CR 116.1, players may activate activated abilities at any time they have priority unless a rule or effect says otherwise. Teferi's restriction extends to activated abilities as well—opponents cannot activate abilities at instant speed while Teferi is on the battlefield.

Specifically, this means opponents cannot activate abilities during your turn (outside of their own main phases when the stack is empty), cannot respond to your spells or abilities with activated abilities, and cannot use activated abilities during combat steps, end steps, or any other non-sorcery-speed window. CR 116.2a and 502.2 govern when players can normally cast instants and activate abilities.

Note that mana abilities are an exception. CR 605.3b states that mana abilities don't use the stack and can be activated any time a player could activate a mana ability. Teferi does not restrict mana abilities because they are a special category governed by their own rules and don't use the stack at all.

Concrete example: You cast a creature spell on your turn. Normally, your opponent could activate a Birthing Pod or tap a creature with a tap ability in response. With Teferi, Time Raveler on the battlefield, your opponent cannot activate those abilities in response—they are locked out of instant-speed activations entirely.

Also, Teferi's second ability lets you cast instant-speed spells as a sorcery restriction does not apply to you, only to each opponent (CR 112.6 distinguishes the controller's own permissions from restrictions placed on others).