This may be a misleading lesson. There appears to be a direct contradiction here:

Question

In: Level B2, Verbs Tenses & Conjugation, Modo indicativo, Modo subjuntivo, Oración subordinada temporal1. Cuando is always used with past
tenses in the indicative ….2. If we use past tenses in the subjunctive with Cuando …There appears to be a direct contradiction above: --------------------------------------------------------------------------------In statement #1, it is stated that Cuando must be in the indicative moodin statement #2, it is stated that Cuando may be in the subjunctive mood.James

Answer

Hola James,
I think you misinterpreted what the lesson is saying. You need to keep reading the whole sentence...
We are saying in the lesson "Cuando is always used with past tenses in the indicative to express when something happened/has happened/had happened". We understand that these actions actually took place, there is no doubt about it."
Then later on we say "If we use past tenses in the subjunctive with cuando, then we are not referring to past events but future or hypothetical events."
So, you can use cuando with both: past tenses in the indicative or past tenses in the subjunctive, but they will convey different things.
We didn't mean in the first explanation that cuando is "always" used with past tenses in the indicative, but that it is "always used with past tenses in the indicative to express..."
I hope this clarified it.
Saludos
Inma