What are the specific conditions for obtaining a Braytech Schematic?

I have done some experiments to speculatively confirm some of the Reddit rumours.

How many Sleeper Nodes do I need to open to get a Braytech Schematic?
Between one and four.

Is the Schematic drop limited to one a day?
In my tests, yes. Once per daily reset. Changing in update 2.5.2.2 on Sept 3rd 2019

Does it matter which nodes I open?
Nope.

Does having the weapons you already have make a difference?
Not for me. I had three weapons in my inventory (AR, Sidearm & Sniper) and got duplicate assault rifles. You're just getting a Warmind Engram, so it's down to RNG.

Farming
You'll want to farm around 12 Resonant Stems per daily reset.

Small sample research data

• Saturday - Opened three nodes, got a schematic on the third one.
• Sunday - Opened three nodes, got a schematic on the third one.
• Monday 1pm - Opened six nodes and did not get a schematic.
• Monday 6pm (After daily reset) - Opened one node and got a schematic.
• Tuesday 10pm (After daily and weekly reset) - Opened 4 nodes and got a schematic.
• Thursday - Opened one node and got a schematic on the first.
• Friday - Opened three nodes and got a schematic on the third.
• Monday - Opened one node and got a schematic first time.

I have marked this as accepted, because this evening I got a Niflheim Frost to complete my badge.

Destiny 2 Update 2.5.2.2

Braytech Schematics
Braytech Schematics are no longer limited to 1 per day, per account
Braytech Schematics have a 25% drop chance when opening any Rasputin Data Cache
The four Braytech weapons offered by Ana Bray, and also tied to the Wayfarer seal, now have a greater chance of granting a weapon you do not currently have.