Most published cases of symptomatic epidural hematoma state that it develops within a few hours after operation. Cabana et al., for instance, reported an average delay of 5.3 hours from the lumbar intervention to the subsequent onset of hematoma symptoms 1).

1)
Cabana F, Pointillart V, Vital J-M, Sénégas J. Postoperative compressive spinal epidural hematomas: 15 cases and a review of the literature. Revue de Chirurgie Orthopedique et Reparatrice de l’Appareil Moteur. 2000;86(4):335–345.