Chances are your rewards will be applied on August 18. The day after your renewal date.
You can change your plan early but you have paid to the end of your renewal date (3 days). Since PM is a prepaid plan, you will not get a refund on the 3 days.
You can have it setup now to change the plan on your renewal date.
Yes this is what I believed to be the case too, so unless you have a long time until your next renewal or it really urgent, most people prefer to change on renewal date so not only do they get full bang for their buck on their plan, but they get their rewards in a timely fashion without delay.
it's not each month on 17th renewal,
in here prepaid service for 30 day,
your rewards be applied before is take from your credit card payment and if you change plan on the date renewal, you will get it same as is have before.. and you can check in history payment.
He didn't say he thought it was each month. He just said his next renewal will have been the 17th. He even said his 30 day plan.
He also said he had changed his plan before the renewal (see subject line) so none of the rest of your post is relevant.