Marriott Rewards has offered instant Silver status for employees from various companies several times in the past and they have just reactivated the campaign again.
Members that sign up with eligible corporate email addresses will have their account set up as Silver one instantaneously.
If you happen to work for any other global company, you can change the company name at the end of the UTL to see whether this offer is available for you as well.
Note that you must sign up using eligible company email address (but apparently you can change it to any other email once the registration has gone through) and the Silver status is instantaneous.
This status maps to SPG Preferred Plus that comes with 4PM check out, complimentary internet and basic room upgrade. You can link your accounts and the SPG status is valid immediately once you have done it.
The main benefits when staying at Marriott properties at the Silver level are bonus points, late check out (based on availability) and reservation guarantee.
If one as stays coming up with either Marriott or SPG and don’t have status with either of them, it makes sign up under this offer. It is unclear how long it is valid for.