Once the fundraise has a close date you'll receive a 5-day notice. In addition, you will see a 7-day countdown on the fundraise page. You have up until the fundraise closes to cancel (or 4 days after you invest, if later).
Once the minimum funding target is met, some companies do a "rolling close", where investments that have successfully applied are executed and funds transferred, but the campaign is still open to receive new investments. If your funds are disbursed as part of this rolling close, you may not cancel and receive a refund.
You'll still receive a five-day notice when any close is about to happen.