I have this in my own variation of this file, I've done it by using 2 lay rules and 2 green up rules
Lay A is armed till 30mins and sets signal X
Green A then triggers 20 mins after signal X is set
Lay B is armed 30 mins till 1hr 5mins and sets signal Y
Green Y then triggers 35 mins after signal Y is set
It doesn't give exactly 20mins all the time but you could add further ones depending on how close/precise to 20mins you wanted it
I also have conditions in the green after goal rule so only one or the other can trigger