Background and Objectives: Irregularly sampled intensive care unit (ICU) electronic health records (EHRs) are difficult to transform into reproducible patient-level representations for outcome prediction and external validation. We propose a deterministic multi-temporal tensorization framework for representing early ICU trajectories in stroke patients and evaluate its utility for ICU length-of-stay (LOS) regression and in-hospital mortality classification under strict no-refit external validation.Methods: Clinical trajectories from the first 48 hours after ICU admission were summarized using expanding observation windows of 1, 2, 3, and 4 hours. Within each window, 77 clinician-selected clinical and laboratory variables were aggregated using mean, median, minimum, and maximum values. Age, gender, and race were encoded as time-invariant demographic variables and replicated across the temporal axis. The resulting summaries were aligned to a common 48-step timeline and stacked into a four-channel tensor representation. Tensor-derived tabular features were used to train XGBoost models for LOS prediction and mortality classification. Model development was performed on MIMIC-IV using patient-level splits, while eICU was used as a fully held-out external cohort without retraining, threshold optimization, or recalibration. Performance and calibration were assessed at the patient level, while SHAP-based interpretability was performed on the internal MIMIC-IV test set.Results: For LOS prediction, internal MAE/RMSE were 1.001/1.440 days with R^2=0.590$, compared with 1.199/1.841 days (R^2=0.227$) externally. For mortality prediction, ROC-AUC was 0.925 internally and 0.901 externally. PR-AUC decreased from 0.830 to 0.414 but remained well above the cohort-specific no-skill baselines of 0.204 and 0.064. At a fixed threshold of 0.5, precision decreased from 0.900 to 0.409, sensitivity was 0.554 and 0.581, and specificity was 0.984 and 0.943. Calibration analysis showed external drift, with overestimation of mortality risk (calibration intercept -1.451; slope 0.619) and underestimation of LOS (mean residual bias +0.489 days). Internal-test SHAP analysis identified clinically plausible predictors, including Glasgow Coma Scale, oxygenation and respiratory support variables, and hematologic and inflammatory markers.Conclusions: Multi-temporal tensorization provides a reproducible computing methodology for transforming irregular ICU EHRs into structured representations suitable for scalable machine learning and cross-database validation. Preserved discrimination did not imply transportable calibration, supporting the need for local calibration assessment before clinical deployment.