PurposeTo evaluate the relationship between warm ischemia time (WIT) duration and renal function after robot-assisted partial nephrectomy (RAPN).MethodsThe CLOCK trial is a phase 3 randomized controlled trial comparing on- vs off-clamp RAPN. All patients underwent pre- and postoperative renal scintigraphy. Six-month absolute variation of eGFR (AV-GFR), rate of relative variation in eGFR over 25% (RV-GFR > 25), absolute variation of split renal function (SRF) at scintigraphy (AV-SRF).The relationships WIT/outcomes were assessed by correlation graphs and then modeled by uni- and multivariable regression.Results324 patients were included (206 on-clamp, 118 off-clamp RAPN). Correlation graphs showed a threshold on WIT equal to 10 min. The differences in outcome measures between cases with WIT < vs ≥ 10 min were: AV-GFR − 3.7 vs − 7.5 ml/min (p< 0.001); AV-SRF − 1% vs − 3.6% (p< 0.001); RV-GFR > 25 9.3% vs 17.8% (p= 0.008). Multivariable models found that AV-GFR was related to WIT ≥ 10 min (regression coefficient [RC] − 0.52,p= 0.019), age (RC − 0.35, p = 0.001) and baseline eGFR (RC − 0.30, p < 0.001); RV-GFR > 25 to WIT ≥ 10 min (odds ratio [OR] 1.11,p= 0.007) and acute kidney injury defined as > 50% increase in serum creatinine (OR 19.7,p= 0.009); AV-SRF to WIT ≥ 10 min (RC − 0.30,p= 0.018), baseline SRF (RC − 0.76,p< 0.001) and RENAL score (RC − 0.60.p= 0.028).The main limitation was that the CLOCK trial was designed on a different endpoint and therefore the present analysis could be underpowered.ConclusionsUp to 10 min WIT had no consequences on functional outcomes. Above the 10-min threshold, a statistically significant, but clinically negligible impact was found.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00345-023-04366-3.