I've had this issue a couple of times (most recently this week) and depending on your luck, chat/calling usually comes up with a suggestion to wait 48 hours. However, I've found that asking for assistance on social media gets someone to force an account sync, which makes the points available immediately if they didn't already post. Each time this happened, I'd already received an e-mail confirming that the points purchase had processed and that they were reflected in my account balance. However, I could see points in my activity but the balance was stuck until the manual account sync was initiated.

FWIW, my Hilton account is several years old and has monthly activity.