legality is just as questionable as any other modification like double click or changing hotkey configuration, they all simplify/offload some aspect of gameplay that the player must ordinarily account for themself and thus create an unfair edge for those using it over those not.
it can be interesting to explore the potential of the revised gameplay parameters though (ironically the same argument that usa-archer made for posting hacks on his website, haha. hacks are just unsanctioned mods) -- the most important thing is ensuring that all players in a matchup understand & agree to the parameters up front but we can see that this is already not happening especially in the increasingly common case of modded hotkeys, and people using the double click without disclosing it, etc. at least if people want to play in matchups that prohibit the timer it can be caught in a ss, though of course the next step would be people creating ways to add a timer that can be toggled w/ a hotkey (this can probably already be cobbled together w/ various freely available apps pretty easily without needing some war2-specific tool)
in reality the kind of people who care about playing on an even field will make the effort to do so, and those who don't won't, and there isn't much we can do from a moderation perspective without better enforcement technology. probably most people won't care about using a timer & the ones who are skilled enough for it to make a difference in their playing won't want to play on unfair terms.