The SLC won't stop the screed drying out, but it will take longer, so wait a bit before you do it. You need a 6ft spirit level to determine the high spot of the floor, then work out from there. SLC doesn't actually level itself, and it need help moving it around, and it's best if you have an idea of where the level should be. Having found your high spot, Work outwards in metre square pattern, and drill the floor and use rawlplugs and screws to continue the level from the high spot. Depending on the area, and how hot the day is, you'll need 2 buckets to work with, one person to mix, one to pour the SLC into the bucket, one to lay, and the person pouring the mix into the bucket can then be cleaning the previous bucket out, and filling it with water. Use a bucket with a line marked for the right amount of water, and maybe add half a litre extra to make it a little runnier, not no more than that. The person laying the SLC will spread it around using a trowel, to the level of the screw heads. If it's a large area, you'll want spiked shoes, and a spiked roller to get the air out.
Damn it, just reread the OP, and noticed the word soon. Read it first as how can this be done. Well, you may already know all of the above, but I'm loathe to delete all my hard work. Best of luck