When I left my devices at work, whenever I had the urge to go on the internet at home, I would realize it would take me another hour commute to get there and back, and that wasn't worth it.
And yet, some people do manage to go cold turkey. And cold turkey is generally easier than a approach based on limitation.
Your one strength here is you know you don’t really need the access, as you already did it. If you want to google something or message someone you can write it down on paper, and handle it in the morning.
Perhaps this truly won’t work. In which case, would any software/hardware restriction work? They can all be circumvented, and fairly easily for someone technical. If you can find one will hard time based limits, that might work. Freedom, or Cold Turkey may be that, I’ve never looked into circumvention difficulties.
But then again, if you really want to try, could you treat yourself as an addict, say there are no real excuses, and force yourself to call someone if you desire to plug it in? Or even say you will plug it in for 10 min for a true emergency but unplug and tell them you did?
I don’t know. All of us have different psychologies. You’ll have to consider what has a chance of working for you. But I’ll end by saying that with a conscious choice it is possible to make a change, and it is often perversely easier to do this at a low point.
Edit: actually, the other commentor’s suggestion of a timer box seems extremely promising. You may want a dumb phone or a landline for emergencies if you do that though. But it has two elements: 1. Impossibility to circumvent 2. Physical separation
Edit 2: one thing that might work is Beeminder. You pay if you fail to meet the goal. And they have a weasel mode.
When you're done work you can pop your stuff in it, set a timer for 16 hours or whatever is necessary then you can't access these things at all.
Here's a rough link to what I mean (https://www.amazon.com/Kitchen-Safe-Locking-Container-Height...)
Seems like my addiction runs very very deep.
Even if you fail every once in a while, it'll be an improvement to what you're describing now.