Hold messages during quiet hours

How to do it

Store an IANA time zone name per user, such as Europe/Stockholm, never a fixed offset, because offsets change with daylight saving. Default to 21:00 to 08:00 and let people change it. The US TCPA allows marketing calls and texts only from 8 a.m. to 9 p.m. local time, and some states are stricter. When you lack a time zone, guess from the phone's country code or the last session, and use the stricter window. Only critical types, such as fraud or safety alerts, skip the hold.

Example

import { Temporal } from '@js-temporal/polyfill';

export function nextAllowedSend(now, timeZone, quiet = { start: 21, end: 8 }) {
  const local = now.toZonedDateTimeISO(timeZone);
  if (local.hour >= quiet.end && local.hour < quiet.start) return now;
  const day = local.hour >= quiet.start ? local.add({ days: 1 }) : local;
  return day.with({ hour: quiet.end, minute: 0, second: 0, millisecond: 0 }).toInstant();
}

from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

def next_allowed_send(now: datetime, time_zone: str, start: int = 21, end: int = 8) -> datetime:
    local = now.astimezone(ZoneInfo(time_zone))
    if end <= local.hour < start:
        return now
    day = local + timedelta(days=1) if local.hour >= start else local
    return day.replace(hour=end, minute=0, second=0, microsecond=0)

How to check

A unit test sets the clock to 23:30 in the user's zone and expects the next send time to be 08:00 the next morning. A second test covers a daylight saving change night.