It is important to have an understanding how data in an Excel spreadsheet is updated when connected to Bet Angel.
A market in Excel will update each time the market data is updated by Bet Angel. If the market is currently displayed in the main application's trading screen then it will update at the refresh rate set. If not, it will update once per guardian refresh cycle.
If you have connected via Guardian and the market is not loaded into Excel then the data will update once per Guardian cycle. For example, if you have 20 markets in Guardian and the refresh is once per second then the connected market will update once every 20 seconds unless the market is the 'live' market as described above.
If you use Guardian you can choose to restrict the refresh cycle to markets set within the time window specified. This will allow Guardian to ignore those markets outside this window and refresh the markets within the window more often. This will speed up the data refresh cycle.
Note that the market start time is as advertised by Betfair. WIth some markets the actual start time may be different such as with tennis markets as these times are approximate start times. Some other events such as horse racing may also be delayed and you will need to take this into account.