Timezone#strftime("%s", time) converts the given time to UNIX time. Because UNIX time is the number of seconds that have elapsed since 1970-01-01 00:00:00 (UTC), the result does not depends on the timezone.

However, the result of the folloing code seems incorrect.

#!/usr/bin/ruby

require 'tzinfo'

jst = TZInfo::Timezone.get("Japan")
utc = TZInfo::Timezone.get("UTC")

time = Time.now.utc

puts jst.strftime("%F %T (%Z): %s", time)
puts utc.strftime("%F %T (%Z): %s", time)

The code returned:

2018-08-30 21:18:23 (JST): 1535663903
2018-08-30 12:18:23 (UTC): 1535631503

In the case above, I expecet the result as:

2018-08-30 21:18:23 (JST): 1535631503
2018-08-30 12:18:23 (UTC): 1535631503

I used tzinfo-1.2.3 with Ruby 2.3.