Only a 1/2 second, and only one time per day, and certain it's a grind and not a squeal. Well,
1. Has there ever been one morning it DIDN'T do this? Extra high or low temp? Rain, dry, fog?
2. Have you wiggled the fan to see if it's contacting the shroud a 1/2 millimeter only when bone-cold? Maybe the clutch fluid settling away from the bearing at night and getting some slop?
3. Do you have a broken mount allowing a jerk between parts, again only when everything is completely contracted?
4. Have you tried parking up or down a steep grade overnight?
As mentioned, stand at the engine every morning and get someone else to start it to track it down.
I once traced a infrequent "chirp" on start-up to the hood strike. It sounded like a belt, or pulley bearing. It took several months to find, and don't recall how I caught it.
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, yes again... LT-4 knock module!