Great advances in experimental physics are being made using attosecond pulses of XUV radiation, where it is possible to initiate and control photoelectrons from atoms in real time. A natural question then arises: Is it possible to use these pulses to measure the time it takes for a photoelectron to be ionized? It is well-known from quantum theory that time is not an observable quantity. Here, our aim is to discuss what temporal aspects of photoionization can be measured in these experiments.