I may give it a whirl this weekend with my kids, but I'll see how it goes. The issue with most of these strategies is that kids are generally good penetration testers in their own (limited) way; if one means of accessing the internet is blocked, they'll use another one; given that they have access to different devices and no universal management system, I think they will just flip to another device.
Don't get me wrong, I think things like this are a useful tool in the arsenal of a parent who cares about their child's upbringing. I always find it slightly depressing when I see comments such as "this isn't a replacement for being a real parent", etc., which always seem to come with the subtext of [like i am] to them. I don't think anyone who would care about this sort of thing would think it was a replacement. I'm a step-parent to 4 kids (18,16,13,11) and it is a difficult task to get them onside in terms of what I see as responsible internet usage (which increasingly comes down to not only time, but the kind of sites and apps they are using), and most importantly what's easiest referred to as 'screen time' - games, etc. As mentioned above, if you do manage to lock something down in terms of time, then they'll use something else. And I really care about this, but it's a difficult thing to police in terms of actual effort, attention and also expectations. I don't think it's healthy for them to spend all their time on any kind of device, so we go out for walks and do activities when we can, and Sunday afternoon until Monday breakfast is no devices for ANYONE at all (Us included, which has been a real success after the initial resentment and whining), but often real life or work gets in the way, and having a way of enforcing limits of usage or actively promoting worthwhile usage to gain credits for trivial use would be a good thing to do, IMO.
But I'm yet to see anything which comes close to doing it; I did have a router running Gargoyle a few years ago, with each device in an appropriate group, and times enforced, but it couldn't handle that many reservations and crashed enough to make it more trouble than it's worth. That's compounded by the older kids having their own phones with some (limited) data plan, which can of course get round any restrictions. Promoting a 'stop using your device an hour before you go to bed' can be wearing, no matter how good your intentions, and how pleasant the kids may be.
In short, unless there's a universal standard for this, and everyone signs up to it (across all manufacturers and devices), I think it will have limited success, alas.