(Add two conditions so the marker appears after 10pm -- to match dialogue condition -- and only when J'skar is invisible.)
Target #1, VolanaroRef
Equal to 40, GetStage MG06Bruma
ADD Greater than or equal to 22, GetCurrentTime
ADD Not equal to 2, GetQuestVariable MG06Bruma, invis
(ADD target so the marker points to J'skar after becoming visible again -- need to talk to him to continue the quest.)
Target #5, JskarRef1
Equal to 40, GetStage MG06Bruma
Equal to 2, GetQuestVariable MG06Bruma, invis
I considered using the MG06Bruma.JskarVisible variable, but invis provides a better solution.