With a start point of 20 CYA and the amount of time you will be gone I don’t think you should have too much of a problem. The release rate from the chlorine floater with an 18 ft intex should be very low so I am sure the amount you build in CYA will not too great. With out a starting point of your pH and ALK it would be hard to really pinpoint your need to preadjust your ranges but if you are on the high side of normal on both I think you will be alright due to the low release from the floater. So what I would do.
Check your chemistry.
If ALK is normal on the high end leave it alone. If low adjust up slightly.
If pH is low adjust up but stay with normals.
I don’t know the settings on the specific floater but check the instructions and set for maintance dose
Tie the floater like I posted previously.
Pack up and go on vacation. Have fun and enjoy a margarita for us.
Steve