We noticed that time_remaining is for the current phase of the round, not for the round itself. Will it always be like that?

CurrentRoundState.time.time_remaining is the countdown of the current phase; except after the bomb is planted, the "current phase" becomes the bomb. So once the bomb is planted, time_remaining switches to counting down to detonation (and to defuse completion during a defusal) – while info.round_type still reads IN_PROGRESS. The feed doesn't expose which countdown type is running via this field itself; you should disambiguate using the bomb_state.