Yep a good voice recording app serves two fold. It allows you to play back the audio to be accurate on say upsell suggestions, and it can give you an accurate timer, because you can hear the events take place. A good recorder will even give you a time and date stamp so you know exactly what time the recording began which is handy when the form asks "what time did you enter the store." "what time did you leave."
Having the recording going with the phone either on the table on in your shirt pocket is a bit less suspicious and less awkward than just a timer you may have to look at several times during the meal.