How long is your credit eval good for

[dfrecore]

I'll tell you how it works for TESU. The other two are similar. Once you apply, you get to have two batches of transcripts processed and put onto your evaluation. You stay locked into your catalog (which is what the eval is based on) for a year. If you register for at least one course during that time, you are then considered enrolled and a new one year time limit starts. As long as you either take another course or TECEP, you keep extending your enrollment.

COSC and EC work differently than TESU in terms of enrolling.

For COSC, if you enroll, you start paying per-term fees (currently $319 with a discount) - so you do NOT want to enroll until you are ready to take your cornerstone and capstone.

For EC, if you enroll, you have to pay the Enrollment Fee of $1095, and then if you're not done within a year, you pay $495 for another year.  Again, you do NOT want to enroll until you're ready to take your capstone.  The only caveat here is that it looks like EC is adding a cornerstone beginning Jan 1 2020, so you would probably want to enroll prior to that in order to get in under the current plan without the cornerstone.
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And I agree that you're better off enrolling at one of the Big 3, and then getting a MA degree.  If you list your courses here, I can help tell you which way you might want to go.