Can you sacrifice a land to pay for a cost during your opponent's turn?

Sacrificing a permanent, including a land, is a type of cost that can be paid at instant speed whenever you have priority — which includes your opponent's turn. There is no rule restricting when you may sacrifice a permanent unless the card itself specifies a timing restriction (e.g., 'activate only as a sorcery').

Under CR 509.2, costs are paid as part of the process of casting a spell or activating an ability. CR 118.12 confirms that paying a cost of sacrificing a permanent simply means moving that permanent from the battlefield to the graveyard as part of paying. Neither rule limits this to your own turn.

Many activated abilities require sacrificing a land or other permanent as part of their cost, and these can be used at instant speed on any player's turn. For example, the classic Zuran Orb says 'Sacrifice a land: You gain 2 life.' This is an activated ability with no stated timing restriction, so it can be activated on your opponent's turn, in response to a spell, etc.

The only exceptions arise if: (1) the card says 'activate only as a sorcery' or uses similar language restricting timing; (2) an effect such as Teferi, Time Raveler's static ability prevents you from activating abilities at instant speed; or (3) you simply do not have priority at the moment you want to act.

Concrete example: Your opponent attacks you with a 3/3 creature. Before blockers are declared, you activate Maze of Ith's ability — but first you need mana. You sacrifice a land to Lotus Field's ability on your opponent's turn during their combat phase to generate mana, perfectly legal since you have priority and the ability has no sorcery-speed restriction.