Since you're generating the same output as the 'date' command provides, you could just do it right from the command line:

$ date; ./myscript; date
[download]

You could also create a macro in whatever editor you're using that would let you stick something like this at the top of your scripts:

sub x{print localtime()."\n"};BEGIN{x};END{x}
[download]

Not that I'm not actually recommending this as a *good* solution; I suspect you're having an XY Problem, with the concomitant incorrect approach. But since that's not the question you asked...