What to do if time is bad, but repotting is a must?
Sometimes an orchid desperately wants repotting for the reason that the combination is so deteriorated or the plant is badly overgrown. Waiting until the suitable cycle to repot could imply that the resulting root damage may well harm the plant more than repotting could. Be as gentle as possible with plants potted out of time, watching them carefully afterward. If you find that the roots are rotten, wipe the roots and pot the plant into a very small pot, and wait until the ordinary repotting time to repot as usual. Never overdo the watering, but give as much humidity as possible.
If the plant is overgrown but the mixture is still good enough, a procedure known as "dropping on" is effective. Take out the plant from its overgrown pot and place it, mix and all, into a larger pot. Then put in fresh mix to fill gaps. Dropping on disturbs roots very small and is an satisfactory way to repot even at right times if the mixture is still fine. Orchids that prefer a rather decayed mix (such as Cymbidium) do better being dropped on, with a full repotting only each other time.
Another effective trick for overgrown sympodial plants climbing over the side of the pot is to place another same height pot next to it to accommodate the hanging pseudo bulbs and roots. The second pot should be plastic, so that you will be able to cutaway a V-shaped piece of the rim so it will fit better under the overhanging growths. Position the next pot below the new growths and roots hanging over the side of the new pot, and fill it with new mix up. Then tape the 2 side-by-side pots together around both rims, to stop the new pot from moving. The overgrown pieces will be able to establish in the new pot without too much disturbance. As soon as the appropriate time arrives, the whole plant can be reported into a larger pot, or easily divided, with a natural break at the point between the 2 pots.
Another time you should avoid repotting your orchid is when it is in bud or flower. Wait until flowering is over, because repotting can cause enough trauma to make the flowers or buds drop off. If the orchid has a flower sheath with no buds evident inside, or if the spike is still short and budless, feel free to go further on if required. Newly acquired plants might require repotting if the mix is noticeably deteriorated or the plant is overgrown. Nevertheless, give new plants at least a month to adjust themselves to their new growing conditions prior to repotting, to allow recovery from the shock of a new environment without the added trauma of repotting.