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@wtf is deeply involved with Flux and found a suggestion at Transitioning from InfluxDB 1.x InfluxQL to 2.x Flux query language - #4 by koenwindey - Grafana Support - Grafana Labs Community Forums about how to optimally perform datetime offset calculations with Flux.
import "experimental"
import "date"
OffsetStart = experimental.addDuration(d: -37h, to: date.truncate(t: now(), unit: 1d))
OffsetStop = experimental.addDuration(d: -13h, to: date.truncate(t: now(), unit: 1d))
from(bucket: "yourbucket")
|> range(start: OffsetStart, stop: OffsetStop)