Normally the recommended cure time for SG is at least 24 hours before you top it with anything...and that includes more layers of SG. You may find that it varies, but this is a common number.
What do you guys do before applying that second and third layer if the vehicle has been used? I'm assuming you wash it if it's dirty. However, is QD ok if it's just dusty? Any brand best for use with Klasse?
Yeah use Sonus since it's acrylic as well. Just avoid any QD that contains carnauba since the SG will have problems bonding with carnauba underneath. I believe Megs Final Inspection is OK to use too.