If you'll need the extra money in 2-3 years, then you need it now. Don't wait.

Save as much as you possibly can over the 2-3 years, and the needs at that time will be less of a burden.

It's MUCH easier to earn the money early than to wait till the last minute (day, month, whatever).

Doing something about it now also gives you a margin for error:

Scenario 1: You wait 3 years, till you need the extra money. You get a new job. It pays well, but sucks as a place to work. Your new boss is a nightmare. You don't dare quit, because you can't afford to. The stress leads to mistakes at work, and three months after you start, you're fired. And now your unemployed and really, really screwed.

Scenario 2: You get a better paying job now. It pays well, but sucks as a place to work. Your new boss is a nightmare. You immediately start shopping around for something better. You have less stress, because you have some time to find something better. Even so, three months later, you're fired because the boss is just that evil. You still have 2.5 years (or so) to correct the situation.

Those are worst-case scenarios. Here are more likely cases:

Scenario 1: You wait 3 years, till you actually need the extra money. You get a new job. It's tough, but you learn as you go, and you do okay. Day-to-day expenses are a bit rough, and you have no significant savings to fall back on if you have an emergency, but income is adequate to then-current needs.

Scenario 2: You get something better paying now. It's tough, but you learn as you go, and you do okay. You save the excess for 3 years (invest, savings account, money market, whatever). Three years later, when expenses go up (as predicted), you can't continue to save as much, but you have a rainy-day fund set aside for emergencies. Plus, since you have 3 years experience at the better paying job, you are in a better position for higher raises, or another move up to something even better.

If you can predict a future need, start acting on it now. Don't procrastinate on it. If what you're making now would be adequate for the forseeable future, that's one thing. But if it's not, don't delay.

Don't wait for tomorrow to happen, create your tomorrow the way you want it.