If the Navy or Draper says a system can find a star in broad daylight, I tend to believe them
The SR-71 proved that beyond question, though to ease alignment they used a light source in the hangar ceiling for initial alignment, helpful no doubt in the typical UK weather.
A hot alignment took 18 minutes, cold 36 minutes, exclusive of warm up time. A scramble would of course require an inflight alignment. Catalogue had data for 61 stars, sun, moon and planets were excluded. Until the star tracker had a lock nav was by inertial.