Not sure what you mean by “how much of a buffer”, but this much I can tell you - Having and maintaining a valid status throughout the process is highly encouraged as it enables one to have a fall back status should in case the AOS petition gets denied for any reason. If your non-immigrant current status expires while waiting for AOS interview, you automatically roll into what is known as adjustment pending which is also a valid status for as long as the AOS petition is pending.
I see. At what point of the process will I be rolled into the adjustment pending status? Is it when the lockbox receives my AOS package?