AkkaTip.scala

....
  val days = 3
  val lastTimestamp = OffsetDateTime
    .ofInstant(
      Instant
        .ofEpochSecond(timestamp),
      ZoneId.systemDefault()
    )
    .truncatedTo(ChronoUnit.DAYS)
  val nextScheduleTimestamp = lastTimestamp.plusSeconds(days * 24 * 60 * 60)
  val duration = nextScheduleTimestamp.toEpochSecond - OffsetDateTime
    .now()
    .toEpochSecond
  if (duration > 0)
    timers.startSingleTimer(
      SomeTimer,
      SomeMessage,
      duration.seconds
    )
  else
    context.self ! SomeMessage
  ...