class(var_data)
    [1] "tbl_df"     "tbl"        "data.frame"
    var_data
    A tibble: 42 x 2
       date                Tourists
       <dttm>                 <dbl>
     1 2006-03-01 00:00:00   55280.
     2 2006-06-01 00:00:00   84392.
     3 2006-09-01 00:00:00  132714.

var_list_DB$var_last[ii] <- var_data[last,"Tourists"]
    var_list_DB$var_date_start[ii] <- var_data[1,"date"]
    var_list_DB$var_date_last[ii] <- var_data[last,"date"]

var_date_start   var_date_last  var_val_last
    951868800        1496275200      10044.3162

as.Date(var_data[last,"date"], format = "%m/%d/%Y")
    Error in as.Date.default(x, ...) :
      do not know how to convert 'x' to class “Date”

last<-3
as.Date(as.character(var_data[last,"date"]))
[1] "2006-09-01"
> as.POSIXct(as.character(var_data[last,"date"]))
[1] "2006-09-01 CEST"