Now that I completed BLC, when will I know if it got updated on my ERB/SRB?

HRC does its pull of all the data on the 8th of the month. That means your BLC graduation needs to be updated on your ERB by that date. Not that BLC is listed in your school's section, but that the portion above that says BLC/GRAD. It usually takes NCOAs a week or two to update all their graduates.
Whatever was on your PPW on the 8th is what is pulled. HRC will determine how many E5s they need to promote that month and set the points low enough to pick up that many people. Based off the info they pull, they will release the names around the 25th of the month.

Submit your DA Form 1059 through your chain of command. You can check your iPerms as well to see when it goes in. Just an fyi, having BLC done and a bunch of promotion points does not guarantee promotion, as there is a list of others up for promotion and your unit's need for NCOs. Best of luck brother

I hate to say it, but there is no guarantee that you will get promoted at all with BLC completion: I completed WLC (What BLC was called before) in late-2012, and yet, the Army still has yet to promote me eight years later, with one new Master's Degree and a civilian career much more advanced than any E-4 paygrade equivalent..