See help index "command syntax". If you want to use variables, you are best learn the new script syntax and use
timer.set("-e 0 0"++a)
But if you do not plan to do much scripting, you can also use the & syntax described in the help topic above.
--- In firstname.lastname@example.org, "diamantsus" <diamantsus@...> wrote:
> I would to set a timer with input value and start it.
> i tryed this code but not work.
> Do it is possibile to do?
> a= inputdefault("10","Seconds")
> *Timer Set -e 0 0 a
> *Timer StartStop e