After switching on the devices, they need some warm up time. Lamps of UV or DAD detectors need to be warmed up for approximately 30 minutes to ensure a stable baseline. The flow cells of RI detectors additionally need to be flushed with the solvent to avoid air bubbles and to adjust the zero glass. Furthermore, the HPLC column also needs time to equilibrate properly.
The equlibration time of a column is dependent on the column dimension/column void volume and used flowrate. A column in a dimension 250 x 4 mm ID has a column void volume of aproximately 2.8 mL. So it takes about 14 minutes at flowrate of 1 mL/min to flush the column with five times the column volume.