You can make up quiz points at any time, even before you miss them. The points for forum contributions are just added to the sum of your quiz points. It is quite common for students to realize at mid-term that their quiz average is hurting and make up for some long-ago missed quizzes. If you know ahead of time that you will miss class (for example because you are on an athletic team with an away game) you can chat on the forum to make up for it before you miss it or you can do it later.

Although you can put off making up for missed quizzes, it is not a good idea to put it off for too long because the per-day limit might make it impossible for you to get the points that you need before the forum closes for the semester. Also, it is much easier to post forum contributions when you really have a question to ask or see a question you can answer than it is to make up a bunch of them because you need the credit.