I personally look back at previous years to get an estimate on the processing time for the background screening and I submit it so that it will be completed on or pretty close to the day that my old NSA certification expires. I also don't take the test until the day that my old NSA Certification expires, that way my new certification will begin right on or a day or two after my old one expires. Most of my work comes directly from title companies and they really don't give a flying flip about the NNA NSA certification stuff. And I am OK if I am not "certified" for a day or two - honestly the signing companies that I work with will still use me, if they question my recently expired NSA Certification I let them know that I have already taken and passed the test and that I will have the updated certification in a day or so, I've never had a problem.
I am not going to give the NNA a dollar more than necessary or lose a single day of what I've paid for because of their sneaky shenanigans!