The answer you seek is contained in Appendix c, page 27, of my article "Frozen in Time" which has been posted in the resources section of this forum for about a month now. In my research, plates sensitized with iodine and bromine and held for 2 minutes up to 8 hours before being exposed and developed with mercury, actually tended to get more sensitive with time. Iodized plates keep even longer, especially if kept dry. In 2002 I took the Daguerreian Society group portrait on plates which had been sensitized 4 days earlier. Sealed in plastic bags and kept cool, they survived a 4 hour flight (2 stops) from Chicago to Sacramento California in my carry on luggage. After taking the Dag the plates were shipped back to me in Chicago in an ice cooled container and developed successfully 2 days later. The results appeared on the cover of the Daguerreian Society newsletter Vol. 14, No 6.
APPENDIX C
SENSITIVITY CHANGES IN DAGUERREOTYPES PLATES AFTER COATING
Four quarter plates were fumed simultaneously for 15/10/5 seconds over I/Br/I under approx 1fc of light at approximately 18 C. A 3rd I fuming of 2 sec was done under a safelight. The plates were exposed 2 min, 15 min, 2 hours, and 8 hours after coating to a grayscale illuminated by 2-#2 blue photofloods approx. 15 inches from the gray scale. Incident light was 40 foot-candles. Plate 14 shows the 2 min. plate (Plate 14a), the 15 min. plate (Plate 14b), the 2-hour plate (Plate 14c), and the 8-hour plate (Plate 14d). To avoid any latent image fading, plate development was begun within 5 minutes after exposure.
The results indicated that the sensitivity of a Daguerreotype plate increases rapidly during the first 15 minutes after coating and reaches a plateau within 2 to 8 hours after the fuming process. The data confirms that the aged plates were slightly more than twice as sensitive to light as the freshly prepared plate.