Purpose The timing of treatment for Gartland type III supracondylar fractures has been an area of contention as it was previously thought to be a surgical emergency. The aim of this systematic review and meta-analysis is to clarify whether there is a difference in perioperative outcomes between early and delayed treatment for Gartland type III supracondylar humeral fractures in children. Methods Literature search and study selection were performed according to the PRISMA process. The early surgery (ES) and delayed surgery (DS) groups were defined by the authors of each study included, based on the time to surgery. The primary outcome was the risk of conversion to open reduction. The secondary outcome was perioperative complication risks. Results A total of 14 studies met the eligibility criteria ( n = 1263 patients), of which 665 (52.7%) patients had undergone early surgery, while 598 (47.3%) had delayed surgery. On meta-analysis, there was no significant difference between ES and DS for the outcome of open reduction conversion risk. There was also no significant difference for the secondary outcomes of post-operative compartment syndrome, iatrogenic nerve injury, vascular injury, and surgical site infection. Conclusion Despite the limitations in the literature, evidence exists to support the notion that a delayed approach to the surgical treatment of Gartland type III supracondylar humeral fractures in children does not result in an increased risk of converting to open reduction and perioperative complications.