The process takes...as long as it takes. Previously an Outland application (which can be submitted from inside of Canada, even if the primary applicant is in Canada) was always faster. Problem being, most that are in Canada want/need to work ASAP, which is why the Inland application and available OWP is more appealing. Now, it may or may not be the case, but based on what you will find in other threads here, the process will likely take a year, possible a bit more.
Unfortunately, there doesn't really seem to be an accurate `window' of how long that takes, but there are factors that may work to your advantage. One is that you husband appears to be a U.S. citizen. While that does not, in and of itself, mean that the process will be faster, it may be so because you are not sponsoring a spouse from a vastly different culture. This is is no way a slam to those that are, but IRCC may have less concern that your marriage is not genuine. After all, you do still need to provide evidence of not only your legal marriage, but the evolution of, and maintaining of, your relationship. This is certainly less than a common-law couple needs, but the marriage certificate alone is far from sufficient.
Regarding his current WP expiring in March, I don't know if he can apply to extend that or not. If he cannot, he can only apply for the Open Work Permit (OWP) once you have received the all important Acknowlegment of Receipt (AOR) email from IRCC. It seems to take a couple of months to receive the OWP, so since you have not yet submitted the SCPLC (Inland) application, he may be unable to work for several months, if the current WP cannot be extended. One option may be for him to work remoteley from Canada, so long as he is not paid in Canadian funds, from a Canadian source and the employer does not have a presence in Canada.
Good luck!
