Do you have to use your activity points in the day you earn em?

Haven't been to a full meeting yet, only a WI every week since ProPoints starts.

Are you able to collect your activity points like before or do they have to be eaten on the day you earn them like the regular points on the new plan?

you can collect them and use them when you want during the week. On the online tracker you have the option to choose whether you want to use the activity points first and then the weekly allowance or if you want to use the weekly first and then the bonus points.