The experiment was designed to evaluate timing of GnRH administration in beef heifers based on estrous status with split-time AI. Estrus was synchronized in 816 heifers across 4 locations by using the 14-d CIDR-PG protocol (CIDR insert [1.38 g progesterone] on d 0 with removal on d 14; 25 mg PGF_2α [PG] 16 d after CIDR removal on d 30; and 100 μg GnRH depending on treatment). Estrous detection aids (Estrotect) were applied at PG on d 30, with estrus recorded at 66 and 90 h after PG on d 33 and 34, respectively. Treatments were balanced across locations using tract score and weight. Timing of insemination was based on expression of estrus 66 h after PG. Heifers in each treatment that exhibited estrus by 66 h were inseminated; whereas, AI was delayed 24 h until 90 h after PG for heifers failing to exhibit estrus by 66 h. Heifers in treatment 1 were administered GnRH 66 h after PG irrespective of estrus expression; whereas, in treatment 2, heifers were administered GnRH coincident with delayed insemination only if not detected in estrus at 66 h after PG. Data were analyzed using PROC FREQ in SAS. There was no effect of treatment on overall estrous response (1 = 85%; 2 = 87%; P = 0.49) or AI pregnancy rate (1 = 55%; 2 = 58%; P = 0.54). There were no differences between treatments in estrous response at 66 h (1 = 70%; 2 = 69%; P = 0.64); and pregnancy rate resulting from AI for heifers inseminated at 66 h was not influenced by GnRH (1 = 62%; 2 = 64%; P = 0.65). Furthermore, there were no differences between treatments in estrous response during the 24 h delay period (1 = 50%; 2 = 58% P = 0.22), or pregnancy rate resulting from AI (1 = 40%; 2 = 44%; P = 0.55). In summary, when split-time AI is used in conjunction with the 14 d CIDR-PG protocol, administration of GnRH at AI to heifers that exhibit estrus by 66 h after PG is not warranted. These data suggest, however, that among heifers for which AI is delayed based on failure to exhibit estrus by 66 h after PG, timing of GnRH administration (66 vs. 90 h after PG) may be more flexible.