Minute prices

@valerio.gemmetto
I think you might be confused about daylight savings time, as I don't see any discrepancies. The market open for US stocks is always 9:30 am New York time. On 25 Oct 2018 9:30 am New York time is 13:30 GMT, as 25 Oct 2018 falls within daylight savings time period, which in the US ran from 11 Mar 2018 till 4 Nov 2018, and during which period New York time = GMT - 4, as opposed to standard New York time = GMT - 5, which runs from 4 Nov 2018 till 10 Mar 2019.
On 25 Oct 2018 US market open was at 13:30 GMT. Today it is at 14:30 GMT.
The example of get_timeseries method you included returns an error because start_date and end_date parameters that define the boundaries of the time range requested cannot have exact same value.
Intraday timeseries for composite RICs such as IBM, TRI, AAPL.O etc include pre and post market trades. When you request minute bars for AAPL.O, which is one of the most liquid stocks, the first bar for the day will most likely have the timestamp of 12 am GMT. During daylight savings time this corresponds to the end of the previous day post market session that terminates at 8 pm New York time, and you won't see the next bar until 8 am GMT (4 am New York time when the pre-market trading starts). Outside of daylight savings time the bar at 12 am GMT corresponds to post trading at 7 pm New York time and the bars will continue until 1 am GMT and then stop until 9 am GMT.
The timeseries for NYSE RICs such as IBM.N, TRI.N etc include only regular market session trades, therefore the first bar for the day for these RICs will be timestamped 13:31 GMT or 14:31 GMT.
With regard to the discrepancies in minute bars you mentioned in your original post, if you still see them, would you mind providing a very specific example including the RIC, the timestamp on the bar and the values? A screenshot might be even better.