To my experience plants acclimate to brackish slower than fish (brackish fish kept in fresh).
I'd go with hoppy and offer weeks, if not months for the process.
Some plants, like Vals, seem to take a quicker pace well, but most plants I've tried, take painstakingly long to adapt.
Good luck anyhow.
How high are you intending to go with the salinity and which plants are you trying?
"There is no name for what I'm going to be when I get big."
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Earth. I think we can make a buck on it so let's destroy it.