The short answer: daily while the coat is dropping
A long-haired rabbit in full moult is shedding its undercoat into a coat that is still long, and that combination felts fast. Loose strands tangle into the standing coat within a day or two, and the rabbit grooms the rest off itself, swallowing hair it cannot cough back up. Daily grooming during the moult breaks that cycle: you lift the dead coat out before it mats and before it reaches the stomach. Ten unhurried minutes a day achieves more than an hour once a week, because the hair you remove on Tuesday is hair that never becomes Wednesday's tangle. With a light moult, every other day can hold the line — but let the coat, not the calendar, decide.
Reading the coat to set your rhythm
Run the back of your hand slowly against the lay of the fur each morning. If it comes away carrying a film of loose hair, or you can see the tide line where old coat meets new creeping across the shoulders and hindquarters, the moult is active and daily sessions apply. Check the trouble zones with your fingers: behind the ears, under the chin, along the belly skirt and around the tail, where long fur felts first. When a week passes with the brush coming away nearly clean and no new tide line, you can step down to the between-moult rhythm of two or three comb-throughs a week.
What each daily session should cover
Part the coat and work in sections from the roots outward, so you are clearing the undercoat rather than skimming the surface. Start along the back and sides where the moult runs heaviest, then the chest and skirt, saving the face and ears — where your rabbit is most sensitive — for last and using only fingertips or the softest brush there. Support the skin with your free hand throughout; long coats hide how much a brush drags. End each session by checking for droppings changes and topping up hay, since a gut kept moving is the other half of moult care.
When daily grooming is not enough
If, despite daily work, the coat felts into mats against the skin, or your rabbit strongly resists being handled for medical reasons, a groomer experienced with rabbits can clip the coat shorter for the season — a practical reset, not a failure. Watch for the moult's warning signs while you groom: droppings shrinking or chaining together with hair, a rabbit eating less hay, or bald patches where the new coat is not coming through. Bare skin that stays bare, or heavy dandruff with scratching, deserves a vet visit rather than more brushing, since coat problems in rabbits often start with teeth, weight or skin trouble underneath.
Keeping the daily habit alive for the whole moult
A moult can run for several weeks, which is longer than good intentions last unaided — and the neediest days are often the ones where work or travel intervenes. Rope the household in: anyone who can brush gently can take a day, as long as they follow the same section-by-section routine and stop at tangles rather than pulling them. Setting the groom as a daily recurring task in KinsLe's Care Teams, marked off with a timestamp each time it is finished, means a helper covering for you can see at a glance whether today's coat was already done.