A 59-year-old woman undergoing chemotherapy for breast cancer presents with a temperature of 38.7°C, rigors and a blood pressure of 90/60 mmHg. Her neutrophil count later returns as 0.2 × 10^9/L. She is treated for neutropenic sepsis and stabilises. Which of the following best describes the recommended timing of antibiotic administration in suspected neutropenic sepsis?