Falling participation rates is one of the most significant challenges facing survey research today. To curb this negative trend, scholars have searched for factors that can increase and decrease citizens' willingness to participate in surveys. In this article, we investigate the timing effects of survey invitation e-mails on participation rates in a university-based online panel with members of the Swedish public. Through two large-scale experimental studies, we examine whether the day of week (N = 11,294) and time of day (N = 47,279) for sending out survey invitations impact participation rates. We also ask respondents when they prefer to answer surveys. We find that the timing of survey invitations affects participation rates, however, the effects are small, short-lived, and even out within a week. We also find that the effects of timing vary by employment status and age. The results have implications for scholars and practitioners who utilize online panels for web surveys. When quick answers are important, there may be some limited gains of tailoring the timing of the survey invitation to different individuals. In surveys with more extended field periods, however, such efforts seem less warranted.