Marinating is often described as flavour soaking inward, which is not what happens. Understanding the actual mechanism explains why some marinades need hours and others are wasted after twenty minutes.
How far a marinade actually reaches
Meat is dense and largely made of water held inside muscle fibres. Flavour molecules from a marinade move into it slowly, and most travel only a few millimetres even over a long rest.
Aroma compounds from spices are large and move slowest of all. They stay close to the surface almost regardless of how long the meat sits.
What this means in practice is that a marinade seasons an outer layer and does very little to the interior directly.
Why salt is the exception
Salt ions are small and dissolve readily, so they migrate further and faster than anything else in the mixture. Given enough time, salt reaches well into a thick piece.
Once inside, it changes how muscle proteins hold water, allowing them to retain more of it during cooking. The meat then loses less moisture in the pan or tandoor.
That water retention, rather than surface flavour, is the main textural benefit a long marinade delivers.
What yogurt marinades do differently
Yogurt brings mild acid and calcium along with its proteins, and the combination loosens the connective structure near the surface more gently than a strong acid would.
Its thickness also matters practically, since it clings to the meat instead of running off. Spices suspended in it stay in contact rather than pooling in the bowl.
When the meat hits high heat, that coating dries and browns into a distinct crust, which is central to tandoori-style cooking.
Why longer is not always better
Acidic marinades reach a point where the surface proteins have denatured so far that the texture turns mushy or chalky rather than tender.
Lemon and vinegar cause this fastest, and small or thin pieces are most vulnerable because the affected layer is a large fraction of the whole.
Yogurt is far more forgiving, which is one reason overnight marinades in Indian cooking are usually yogurt-based rather than citrus-based.
What the rest before cooking is for
Meat taken straight from the fridge cooks unevenly, since the outside overshoots while the centre is still catching up from a much lower starting point.
A period at room temperature narrows that gap. It also lets surface moisture evaporate, and a drier surface browns sooner and more completely.
Wiping off excess marinade before cooking serves the same purpose, because a wet coating spends the first minutes steaming rather than colouring.