This code system http://hl7.org/fhir/v3/TimingEvent defines the following codes:

LvlCodeDisplayDefinition
1ACACbefore meal (from lat. ante cibus)
1ACDACDbefore lunch (from lat. ante cibus diurnus)
1ACMACMbefore breakfast (from lat. ante cibus matutinus)
1ACVACVbefore dinner (from lat. ante cibus vespertinus)
1CCDescription: meal (from lat. ante cibus)
2  CDCDDescription: lunch (from lat. cibus diurnus)
2  CMCMDescription: breakfast (from lat. cibus matutinus)
2  CVCVDescription: dinner (from lat. cibus vespertinus)
1HSHSDescription: Prior to beginning a regular period of extended sleep (this would exclude naps). Note that this might occur at different times of day depending on a person's regular sleep schedule.
1ICICbetween meals (from lat. inter cibus)
1ICDICDbetween lunch and dinner
1ICMICMbetween breakfast and lunch
1ICVICVbetween dinner and the hour of sleep
1PCPCafter meal (from lat. post cibus)
1PCDPCDafter lunch (from lat. post cibus diurnus)
1PCMPCMafter breakfast (from lat. post cibus matutinus)
1PCVPCVafter dinner (from lat. post cibus vespertinus)
1WAKEWAKEDescription: Upon waking up from a regular period of sleep, in order to start regular activities (this would exclude waking up from a nap or temporarily waking up during a period of sleep) Usage Notes: e.g. Take pulse rate on waking in management of thyrotoxicosis. Take BP on waking in management of hypertension Take basal body temperature on waking in establishing date of ovulation