This page shows the best observability of 100P-Hartley over the next few months. The graph will show the time of culmination (highest altitude) unless this would be during daylight, in which case the height shown is at dusk or dawn. Hover over a point to see the time and date. Be aware that asteroid orbits are not always stable and so this data is unlikely to be reliable beyond about 100 days.
Note: the data are for a central UK location. To adjust for your location see advice here. .