First reading is the bill’s formal introduction. There’s no debate.
Government bills are usually published immediately after first reading.
The clerk reads the title of the bill and a Government whip names a date for second reading.
The whip will often say “tomorrow,” but this is just a way of placing the bill on the list of upcoming business. It doesn’t mean the second reading will actually happen tomorrow. In practice, there are usually two weekends between first reading and second reading.