In reply to qwerty:
##delay_ar[0] will wait for that specific number of clock ticks.
$rose(ip) |-> ##dealy_ar[0] $rose(op) will check that posedge of op should be after delay_ar[0] clock ticks from posedge of ip. If delay_ar[0] is 0 then both ip and op should be asserted as same clock tick.