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

[dp444]

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