I tend to see Cattleyas growing roots when they are dry. I'd put some humidity trays up. Maybe some deep bowls of water, just to raise the humidity a bit. The Oncidium may be tricky. If orchids are not living in the ideal conditions, sometimes they "Hibernate" when all water is cut off, in other words, just stop growing. Remember that these plants (oncidiums) are high in trees in a "cloud forest." If you had a large capacity mister, put on a timer, it would be easier to mist them a few minutes per day for a few days. But 6 days is a bit long for a mister resevoir. Other wise, oncidiums also are subject to long rainless times when they simply live on any moisture evaporating off of tree limbs, leaves etc. Cattleyas are both arborial epephites, and lithophytes. Many of the species catts live in cracks in rocks where the roots are cool and often moist. Mists from rain or the ocean (in the case of Brazilian catts) hit them and are gathered in the little cracks in the rocks. Very small amounts of water are needed. If you had a mister around catts, and a timer, the mister could be left on for a very short time per day, and the catts would get enough water.
Why "a few minutes of mist" and not "hours and hours of soaking?" Because velamin is like a tissue paper. It takes only seconds to become soaked. (Just water a phal root and look at how fast it gets green). Once it is soaked, that is really all it needs all day, maybe even for several days.
What a lot of people going on vacation have done (without misters with timers ) is to put their plants in the bathtub on some kind of a pedestal (like an upturned pot or a short legged table), and fill the bathtub a few inches with water. This creates a massive "humidity tray" where water is constantly evaporating and creating condensation.
Remember with water, you have choices between rain (lots of wasted water), mist, condensation, evaporation, and many other types of watering.
Hope all goes well!
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