Unknown Dosing Histories

I'm in the process of designing a population PK design for a phase II efficacy study. Patients will be instructed to take their study medication three times a day, 1-2 hours before meals. Since this is an out-patient study, complete dosing histories will not be known. However, during each visit to the clinic for PK blood sampling, the patient will be asked to recall the times of their last 3 doses. Here's my question: What is the best way to code the model when the complete dosing history is not known? Some possible options are: i) assume equally-spaced dosing, or ii) assume a standard unequally-spaced dosing regimen perhaps indexed to typical meal times (e.g., 7am, 12noon, 6pm) since patients are instructed to take their study medication 1-2 hours before meals, or iii) for each patient, assume a daily dosing pattern to be fixed between visits based on the times of their last 3 doses prior to their visit to the clinic.