Create convinient way to set time-zone

[iMissile]

I try to create tibbletime through as_tibble_time with dates in local time-zone.
More specifcally, i have time "2018-04-06 08 MSK". ymd_h("2018-04-06 08", tz="Europe/Moscow")

During coercion internal index timezone was set as "UTC". All other functions will work in incorrect way (time shift). It's ctritical for business to support timezone correctly

[iMissile]

I tried to reproduce issue and see that function filter_time did what I suppose, but it works not in obvious way. It's difficult to assume the timezone of filter_time expression. local\UTC?
How it will be calculated at another computer?
Could you add tz param for filter_time?

sample:

> d_df <- tibble(timestamp=c(ymd_h("2018-04-06 08", tz="Europe/Moscow"), ymd_hm("2018-04-06 23:59", tz="Europe/Moscow")))
> dput(d_df)
structure(list(timestamp = structure(c(1522990800, 1523048340
), class = c("POSIXct", "POSIXt"), tzone = "Europe/Moscow")), row.names = c(NA, 
-2L), class = c("tbl_df", "tbl", "data.frame"))
> 
> t_df <- as_tbl_time(d_df, index=timestamp)
> dput(t_df)
structure(list(timestamp = structure(c(1522990800, 1523048340
), class = c("POSIXct", "POSIXt"), tzone = "Europe/Moscow")), row.names = c(NA, 
-2L), class = c("tbl_time", "tbl_df", "tbl", "data.frame"), index_quo = ~timestamp, index_time_zone = "Europe/Moscow")
> 
> filter_time(t_df, '2018-04-06 07:00' ~ '2018-04-06 23:58')
# A time tibble: 1 x 1
# Index: timestamp
  timestamp          
  <dttm>             
1 2018-04-06 08:00:00