They have a good chance at getting really close to picking it up, but they have a much better chance in 2020 if they can build off the good results in 2018 (if that happens), and if they do that they can then control some redistricting and draw districts more favorably.
In 2018, picking up 24 seats is pretty unlikely. Not going to say it won't happen, but unlikely at this point, just because picking up every Clinton district (which realistically isn't going to happen, so they need some Trump districts as well) is too hard when a lot of these guys are incumbents that are way more popular than the president and aren't going to retire.
And we can't even assume that 2018 will be bad for Republicans.