Table 2. Time between initiation of PW2 and PW3.

Period of darkness (ZT)	Mean time between PW2 and PW3 (hr)	St. dev.
16–20.5	22.8	0.76
20.5–1	25.6	0.53
23–3.5	25.4	2.13
1–5.5	30.6	0.29
5–9.5	33.5	2.47
10–14.5	38.3	0.66
14–18.5	42.9	1.00