If your reason for asking whether to buy now or later is just to save on interest, I will buy now, then dump the 20k into the house loan in 2025.

In fact, no need to wait till 20k... can put into the house loan account as the money comes in. There are full flexible and semi flexible loans to choose from, each with its pros and cons.

Full flexible loan gives the most flexibility (duh), but often comes with monthly maintenance fees, and not all banks allow full interest-waiving for the extra money you pump in, unlike semi-flexi loans. For example, Pbb caps at 70% for excess amount you pay, whereas Hlb caps at 70% of remaining principle.