From the UC Rice Blog (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=42838)
The labeled weeds that RebelEX®controls are sprangletop, watergrass (both early and late), barnyardgrass, ricefield bulrush, Monochoria, redstem, ducksalad, California arrowhead, and water plantain. It does not have a water-holding period. The application timing begins from when the rice has one leaf or more, up to 60 days before harvest. Efficacy, as with most products, is better when the weeds are smaller. For flooded fields, it is important to have maximum contact, so it is recommended to lower the water in the field until at least 70% of the weed biomass is exposed, before application.
The product is “rainfast” (meaning it isn't affected by water) within 2 hours, so reflooding quickly is recommended. The label recommends restarting the flood at 3 hours after application, and to have the field completely reflooded within 24 to 48 hours at a maximum. Long drainage periods can encourage additional germination of certain weed species, including smallflower umbrella sedge, watergrass, barnyardgrass, and sprangletop.
Since RebelEX® also contains penoxsulam, it cannot be applied in the same season as Granite GR® or Granite SC®. Doing so will cause significant phytotoxicity to the rice, and will likely impact yields. Clincher® can be applied in the same season, but depending on the rate of RebelEX® applied, the Clincher® application rates will vary, so please refer to the label for rates and timings if planning to also apply both herbicides in the same season. For management of resistance, however, it is not recommended to apply Clincher® and RebelEx® in the same season, as both contain the same active ingredient, cyhalofop. Repeated applications of the same active ingredient (cyhalofop) will select for resistance in sprangletop, barnyardgrass, and watergrass (both late and early).
Remember to always follow all label instructions when applying any pesticide, as the label is the law. Make sure to pay particular attention to the Use Precautions and Restrictions. Consult your local Agricultural Commissioner's Office regarding buffer zones and aerial restrictions, before making any applications.