> If I could speak Spanish, I would spend the next year studying in Mexico
> I'd spend 12 months FROM NOW in Mexico
(generally, and within the context of the choices you've given).
The next <X amount of time> means from now.
"If I was Superman, I'd spend the next 24 hours just flying around". This means I wouldn't wait until tomorrow or the next day.
(or "If I were Superman" if you live somewhere where they insist on the subjunctive form).