Can I subscribe as soon as the registration statement is filed?

No. A securities registration statement takes effect only after a certain period has passed from the date it is accepted.

Under the Enforcement Rules, for public offerings or sales of equity securities the period is in principle 15 days; it is 10 days for shares of stock-listed corporations and 7 days for allotments to existing shareholders or third parties. If an amended statement changing the offer price or other terms is filed, the effective date may be reset.