It works. Use it if it's helpful. Feedback welcome. Enjoy!

#CLASS {Round Time} {enable}
#VAR rt {0} {0}
#TRIGGER "roundtimer" {Q} {#T+ set_roundtime} "" {gsl|nocr}
#TRIGGER "set_roundtime" {q} {
#VAR rt %eval( %gsl( Q)-%gsl( q))
#T- set_roundtime
#T+ rt_iterate
} "" {gsl|disable}
#TRIGGER "rt_iterate" (@rt > 0) {
#T- rt_iterate
#ala {+1} {
rt=%eval( @rt-1)
#T+ rt_iterate
}
} "" {nocr}
#BUTTON 2 {Roundtime: @rt} {} {} {} {@rt} {} {} {Size} {112} {23} {} {} {} {} {} {} {4} "" {Explore|Inset} {} {RT_gauge}
#CLASS 0

M.