Quick summary: Health researchers who follow people for years often chase replies at what they hope is the perfect hour, yet a DePaul analysis of more than 21,000 contact attempts found that recorded time of day had no consistent link with whether a health questionnaire was completed. Weekdays looked much the same, and apparent weekend effects were too thin to guide practice. Teams running mental health and well being studies should put effort into clear invitations, planned reminder sequences, and fair incentives rather than the clock.

Anyone who has ignored a questionnaire in their inbox knows that researchers often have to ask more than once. For studies that follow people over many years, chasing replies costs staff time and money, so knowing the best moment to get in touch would be valuable.

However, new research suggests there may be no perfect hour to send that reminder. After examining thousands of contact attempts, scientists found that the recorded time of day made no consistent difference to whether people went on to complete a health survey.

The study, published in Psychology International, was carried out by Hanna Nguyen and Leonard A. Jason of the Center for Community Research at DePaul University in Chicago. They rebuilt the complete outreach histories of 4,440 former university students who were invited to fill in a health questionnaire between 2020 and 2025.

Participants had originally been recruited as undergraduates at a large university in the US Midwest and were roughly 22–35 years old at follow-up. The questionnaire took about 30 minutes, and those who completed it received a $20 electronic gift card.

Those who did not respond to the first email could be followed up by phone, voicemail, text message, and email, with social media used when other details were invalid. In total, the team reconstructed 21,402 contact attempts, with some people receiving as many as 18.

Rather than looking only at each person’s final contact, the researchers placed every attempt in date order and checked whether the survey was completed within one, two, seven, or 14 days. This matters because outreach usually stops once someone responds, which can make the last contact look more effective than it really was.

Leonard A. Jason, PhD, professor of psychology at DePaul University, said: “We looked at this question because research teams spend considerable effort deciding when to contact participants, yet a person may receive several reminders before completing a survey. We wanted to examine the full sequence of contacts rather than attribute a response to the final reminder alone.”

Across all four windows, the recorded hour of contact showed no meaningful link with completion. Monday to Friday also performed broadly alike, with no weekday standing out as the best day to get in touch.

Professor Jason added: “The practical takeaway is that researchers may not need to worry so much about finding the perfect hour to send a reminder. In our data, time of day had little association with survey completion. That does not mean timing never matters, but it suggests that maintaining thoughtful contact with participants deserves more attention than fine-tuning the clock.”

The weekend told a more puzzling story. In the main seven-day analysis, Saturday contacts were linked with higher odds of completion and Sunday contacts with lower odds, compared with Tuesday.

The authors caution that weekend outreach was rare, scheduled at staff discretion, and involved small numbers. The Saturday advantage also shrank and was no longer statistically significant when completions were attributed in different ways, so neither result should be read as a reason to change schedules.

They also note that contact method could not be consistently recovered, times were logged in Central Time rather than local time, and the sample was mostly female and White. The findings may therefore not apply to older adults or healthcare populations.

The researchers argue that the most useful lesson is methodological, since timing advice can mislead if it ignores the full sequence of attempts. They suggest that clear invitations, well-planned reminder sequences, appropriate incentives, and thoughtful use of contact methods may deserve more attention.

Looking ahead, Professor Jason said: “A useful next step would be a randomized study comparing contact schedules and methods to see which approaches help people participate without burdening them.”

A definitive answer, they add, would require a randomised trial that assigns people to set contact windows and records their local time. Until then, survey teams may be better off worrying less about the clock and more about how they ask.