In response to Earnest (2019) who asserted "too often studies involving time in maths education are divorced from duration, the quantity that time measures…therefore future studies ought to incorporate the experience of duration into the study design" (p. 25), the purpose of this study was to begin mapping possible conceptualizations children have of duration as an attribute of their lived experiences prior to formal, school-based instruction on time. Specifically, the following research question was posed: When reflecting on past experiences, what conceptions do children (grades preK-1, ages 4-6 years old) seem to have about the duration of those experiences, as indicated by their descriptions of duration? Broadening the current methodology for investigating children's durational reasoning, I drew from phenomenology (Creswell, 2013; Hycner, 1999) and clinical interview case studies (Clement, 2000) to explore seven children's descriptions of the duration of their lived experiences. I designed semi-structured interviews questions to promote the participants' representation of past experiences, or mental operations of reconstructing past experiences (von Glasersfeld, 1991) to conceive of duration as an attribute of those experiences, rather than reflecting on in-the-moment durational experiments. Utilizing Wolcott's (1994) "Description, Analysis," and "Interpretation," I distinguished three themes from the participants' descriptions: (a) duration as an accumulation of activities completed; (b) duration as a consideration of a gross quantity; and (c) duration as a result of exertion. From my interpretation of these themes, I postulate a possible development of durational units (von Glasersfeld, 1981) and a correspondence between conception of number (Piaget, 1965) and duration. Additionally, my findings seem to support Piaget's (1969) conclusions of children's development of inner duration through their perceived rapidity and efforts. I discuss implications of my findings for educators, including a possible re-alignment of Common Core Standards (CCSSI: Measurement and Data, 2020) for school-based instruction on time. I conclude with two methodological limitations of this dissertation and suggest future research based on these limitations. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]