Appendix Table 1.

TIME study recruitment and end-of-day (EOD) EMA data collection details.

Recruitment	Rolling recruitment began in March 2020 and ended in August 2021.To recruit participants, we implemented following strategies: (1) sending emails to individuals enrolled in the Happiness & Health Study, a USC longitudinal cohort study of young adults, (2) referrals from existing participants (word of mouth), and (3) contacting participants identified using ResearchMatch, a national health volunteer registry that was created by several academic institutions and supported by the U.S. National Institutes of Health as part of the Clinical Translational Science Award (CTSA) program.
Inclusion criteria	(1) 18-29 years old living in the United States, (2) intend within the next 12 months to engage in (or already engage in) recommended levels of MVPA (≥150 min/week moderate or ≥75 min/week vigorous intensity), (3) use an Android- based smartphone as their only primary personal mobile device with no intention to switch to a non-Android phone, (4) able to speak and read English and (5) plan to reside in an area with Wi-Fi connectivity during the study period.
Exclusion criteria	(1) physical or cognitive disabilities that prevent participation, (2) health issues that limit physical activity, (3) any diagnosed sleep disorders, (4) unable to wear a smartwatch or answer EMA surveys at home, work, school, or other location where a substantial amount of time is spent (e.g., participant would not be able to answer prompts more than 20% of the time), (5) spends more than 3 hours/day on a typical weekday or weekend day driving, (6) owns an Android phone version 6.0 (or older), or if the app will not function on the phone due to other technical issues, (7) currently owns and wears a smartwatch, (8) uses pay as-you-go data plan or data plan with less than 2 GB of data per month, or (9) currently pregnant.
EOD EMA Data collection	Across the 12 months, an EMA question set is prompted on the smartphone at the end of each day asking participants to summarize experiences occurring that day and their plans for the next day. EOD EMA prompts are delivered two hours before a participant’s anticipated sleep time.