The soil environment plays a pivotal role in ecosystem sustainability, but industrialization and intensive agriculture contribute to heavy metal contamination. Portable X-ray fluorescence (pXRF) has emerged as an efficient tool for detecting heavy metal concentrations in soils and sands. This study evaluates the influence of measurement duration on the accuracy of pXRF results across soil and sand substrates. Measurements were performed using a Thermo Scientific Niton XL2 device on meticulously prepared samples with durations ranging from 5 to 220 s. Results demonstrated that optimal analysis times varied between substrates: 180–220 s for soils and 140 s for sands yielded stable and accurate data. Prolonged durations improved the statistical reliability of concentrations, particularly for trace elements like nickel and arsenic, which required extended times for detection. Findings emphasize the importance of calibrating analysis duration to enhance pXRF accuracy and applicability in environmental and agricultural research.