To load messages for some interval, use the command messages/load_interval:

svc=messages/load_interval&params={"itemId":<long>,
				   "timeFrom":<uint>,
				   "timeTo":<uint>,
				   "flags":<uint>,
				   "flagsMask":<uint>,
				   "loadCount":<uint>}

 Сurrent request can’t be executed simultaneously with following requests:

• report/exec_report,
• report/export_result,
• report/get_result_chart,
• report/get_result_map,
• render/create_messages_layer,
• unit/get_trips,
• resource/get_driver_bindings,
• resource/get_trailer_bindings,
• all requests from chapter Export and import,
• account/get_account_history.

 You can find an example of this request in the sample Messages.

Examples of mask and flags usage:

{
	"count":<uint>,				/* messages count */
	"messages":[				/* array of messages */
		{
			...		
		}
	]
}

You can find message formats in the chapter Data format: Messages.