Answer: It is possible to over-water a hibiscus but I think that what you're witnessing is more a reaction to being transplanted than to being over-watered. As soon as the roots establish themselves, the plants should recover. It may not be necessary to water every other day. In fact, your shrubs will prefer deep, infrequent soakings to frequent shallow watering. Try watering them deeply (apply water slowly so it has a chance to trickle down and wet the entire root mass), and waiting 3-4 days, then digging down near the roots to check the moisture level. If soil is still moist 3" beneath the surface, you won't need to water for a few more days; if it's dry, it's time to water; if the soil is still soggy, it doesn't drain well and you may need to address the problem to avoid root rot.
Best wishes with your hibiscus!
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