time precision limited to 1e-6 due to filtering

[kecnry]

if two times are within 1e-6 days (~0.1 s), the filtering logic will likely fail. We could probably push this precision to within np.float64, but may want to consider a more robust solution for filtering on times.

Related to #247 and 7217610c50800237fb4772c286992e824d08c860