(This is directed to everyone)
Or, even easier:
alias ctimer timer 1 $calc($1 - $ctime) $2-
ctimer <ctime> <command>
Or the like.
Yeah, I'd suggest that, because the other code they posted above doesn't make sense, unless they've meant "$ltimer off" instead of "$ctimer off", which would still be wrong and wouldn't work. BTW, with some corrections following that idea, the code would force the parser to evaluate <commands> twice. Not a big deal, but not nice either.
However, your scripts don't support everything /timer supports and that's one of the reasons why I second Doomstars' suggestion. Yes, all the support that is needed can be scripted as well. But the fact is that it'd be not that simple anymore, although not difficult either.. I've been messing with it.
That said, this "No, this can be easily scripted" argument applies to /timer's time support too ("/timer 12:00 1 0 blah"). Following the same functionality shown above, it can be quite easily scripted. Let's drop it then?
No, we're all able to make good use of it, and we can be sure it will always support any incoming changes and additions that the /timer command could suffer. Why? Because it's built-in. Does this bother anyone, given the fact that it can be easily scripted? I don't think so. Would it bother Khaled? I really don't think so. Now if everyone who scripts it has to keep updating it to support new /timer flags, changes etc, would this bother anyone? I think so. At least a suggestion to make it built-in would come to mind.
So why shouldn't this feature be added? You didn't convince me. Show me a script that decently substitutes anything (including an easy syntax) a built-in version would have and I'll still have the updating argument.
I guess that all I said ends up to what Doomstars said.. "keyword: simple". Simple feature, simple use. Not really necessary if you see no problem in scripting it, so then you script it. Some people prefer it built-in with enough good reasons in their opinion. Sorry, "script it" is *not* an ultimate incontestable solution and unfortunately you won't change that. Workarounds are not necessarily solutions to everyone, even less in a "Feature Suggestions" board.