Yes, you could purchase the Agile PrepCast right now and start watching the lessons. The training hours do not expire. However, don't forget that the upcoming price increase for The Agile PrepCast is relatively small. It's around $30.
You said you are joining an agile organization in November in order to acquire the required 1,500 experience hours. If you work on Agile projects exclusively then it will take you 37 weeks to complete this. That means can apply for the PMI-ACP exam in around October of 2019.
We have also had some indications from PMI that the PMI-ACP Exam Content Outline may be updated in 2019 or 2020.
Personally, I would wait and see where things actually fall for you. Who knows, come December you may decide that agile isn't for you.
Until Next Time,
Cornelius Fichtner, PMP, CSM
President, OSP International LLC