```
Filename: 342-decouple-hs-interval.md
Title: Decoupling hs_interval and SRV lifetime
Author: Nick Mathewson
Created: 9 January 2023
Status: Draft
```
# Motivation and introduction
I think there's another issue to address here too: the offset from the Unix Epoch at which the first Time Period begins. According to rend-spec-v3,
"we want our time periods to start at 12:00UTC every day, so
we subtract a "rotation time offset" of 12*60 minutes from the number of
minutes since the epoch, before dividing by the time period (effectively
making "our" epoch start at Jan 1, 1970 12:00UTC)."
But this isn't exactly what the C Tor implementation does. In `hs_get_time_period_num(),` it defines the offset as `sr_state_get_phase_duration()`, which is tied to the voting interval and the constant SHARED_RANDOM_N_ROUNDS (which is 12).
David, do you have any thoughts on the right solution here? Some options are:
* We could document the current behavior.
* We could add a consensus parameter for the time period offset.
* We could define the time period offset as exactly 12 hours in all cases. (I guess this would break test networks though?)
* Something else?
best wishes,
--
Nick