Controversy rages over the consequences of extending poll hours to make voting more convenient. Academics debate how much such accessibility measures affect turnout (e.g. Gronke et al., 2008; Springer, 2012), while policymakers and judges grapple with the effects of extended hours for partisan or discriminatory aims. Such discussions have focused more on the number of hours voting is available than on the specific hours that are chosen. This is somewhat surprising, as poll-opening hours vary substantially across and within countries; changing voting hours may change accessibility for different groups. Age, in particular, is implicated. Older populations typically prefer relatively earlier schedules; the proportion of younger voters may accordingly decrease when poll-opening hours are earlier in the day. This hypothesis is tested below using data from along the time-zone border that divides Kentucky. Eastern Time Zone areas, where the polls open and close an hour earlier relative to the sun, see significantly higher turnout among older populations and lower turnout among younger populations. This has implications for election results and for equality in ballot-box access as populations age across the rich world (Burden et al., 2017). More pointedly, though, given the divergent partisan and policy preferences of voters of different age groups, these results suggest that choice of polling hours may influence substantive political outcomes in ways readily manipulated by electoral rule-makers (Dassonneville et al., 2017). Age and active hours Biology provides reason to expect earlier polling hours to affect the electorate's age distribution. One of chronobiology's most consistent findings is that age correlates positively with "morningness"-i.e. being a morning person-and negatively with "eveningness" (Adan et al., 2012; Carrier et al., 1997; Tankova et al., 1994). Indeed, older people typically perform better on cognitive tasks earlier in the day, while younger people, if anything, reverse this pattern (Schmidt et al., 2007). This helps older people to muster the energy for voting earlier in the solar day, so that having polls open more in the mornings and less in the evenings is more congenial for older than for younger would-be voters. Older people's greater tendency to be (semi-)retired from the workforce further increases their flexibility to vote during the day, putting less pressure on the post-work evening hours. In jurisdictions where election days are not holidays or during weekends, working (or preparing for the workday) typically crowds younger voting-age populations' schedules. Given the widespread preference for voting during