No change in subject after a conjunction, should use infinitive?
 

Hola,

Estoy estudiando para un examen final de español. Tengo una pregunta:


There are a series of conjunctions that often trigger subjunctive like "hasta que." Do I go ahead and use subjunctive if the subject of the first clause is the same as the subject of the second clause?

For example, ¿Cuál es correcto?

"Voy a estudiar hasta entender todo"
I am going to study until I understand it all.

o

"Voy a estudiar hasta que yo entienda todo."

He leído "Ojalá is always followed by subjunctive," but what if "I" am the subject of both clauses?

"Ojalá llegar a tiempo a la clase"

o

"Ojalá que yo llegue a tiempo a la clase"

Are there any good rules of thumb to know when to use subjunctive in the subordinate clause or whether to use the infinitive? Such as "always use the infinitive if the subjects are the same."?

Gracias por su ayuda

Both are OK. The second one -without pronoun (see explanation for the following example)- is the usual one.
The first one lacks a subject (or it lacks a predicative: "ojalá llegar a tiempo a clase se convierta en algo común"). Besides, there's no subordinate clause there.

The pronoun is not necessary in the second instance, even if llegue is both first and third person (the lack of pronoun means a shortcut, that is, first person)

The "exam cheating rules" as I call them, I wouldn't tell you. I'll leave to others to determine your language level and what will work for you.

In the end, Spanish subjunctive is pretty obvious once you learn Spanish indicative and English indicative are quite different. But we can't learn what we aren't taught, can we?

An additional remark:

"Ojalá llegue a tiempo a clase"

is an independent sentence.

It is a nice example to explain how Spanish indicative works: it shows actions actually happening, or they show them happening in some ideation ("¡se va a caer!" ---> it's not actually falling but it represents the notion that such action is the natural consequence of the current situation)

But "ojalá llegue a tiempo a clase" doesn't show my person on time, nor even the notion of me being on time, but the wish that I be on time. The real action in that sentence is the wishing part, and being on time is just the wished object, not an action within the frame of the phrase. That's why subjunctive for that action that is not happening. Of course this situation repeats itself once and again regarding wishes, that's why astray students and teachers say "Spanish subjunctive relates with wishes" or "ojalá triggers subjunctive".

@dp44: You may find useful the discussion about this topic here. :)