Planned Start:

=IFERROR(@IF($F20="End",@GetProjectEnd($C20,$P$9,$P$10,$P$11,$P$12,ROW())+$J20,IF(F20="Start",M20,PlannedStart(F20,G20,VLOOKUP(G20,$B$20:$P$9999,COLUMN(O$19)-1,FALSE),VLOOKUP($G20,$B$20:$P$9999,COLUMN(P$19)-1,FALSE),H20)))+IF(AND($J20<0,$F20="Finish to Start"),$J20,0)+IF($J20>0,$J20,0),"")


Planned Finish:
=IFERROR(@IF(F20="End",$O20,IF(F20="Start",K20,PlannedFinish(F20,G20,VLOOKUP(G20,$B$20:$P$9999,12,FALSE),VLOOKUP($G20,$B$20:$P$9999,13,FALSE),H20,O20))),$L$15)