  Timing requirements for long-range quantum networking are driven by the
necessity of synchronizing the arrival of photons, from independent sources,
for Bell-state measurements. Thus, characteristics such as repetition rate and
pulse duration influence the precision required to enable quantum networking
tasks such as teleportation and entanglement swapping. Some solutions have been
proposed utilizing classical laser pulses, frequency combs, and biphoton
sources. In this article, we explore the utility of the latter method since it
is based upon quantum phenomena, which makes it naturally covert, and
potentially quantum secure. Furthermore, it can utilize relatively low
performance quantum-photon sources and detection equipment, but provides
picosecond-level timing precision even under high loss and high noise channel
conditions representative of daytime space-Earth links. Therefore, this method
is relevant for daytime space-Earth quantum networking and/or providing
high-precision secure timing in GPS denied environments.
