Downsampling to day and week

Can I downsample the measurement to day or week? If so, what’s the time boundaries? 0 o’clock for day and 0 o’clock Monday for week?

You can downsample to day or week using a continuous query. My understanding is that the continuous query will run as soon as the next window of time for the downsampling period arrives, so you would start downsampling from that point on. You can find some more information here.