Dataflows and refreshing to check changes

I have created a dataflow

Every time I do any small developments and then go back to Desktop to refresh, the new column comes through but it doesnt have any data in it.

I have to go back and refresh in Service but it takes about an hour to refresh. This is really causing me issues when i am trying to check quick changes. Its taking me ages to do anything. 

Is there any tips you can give me for avoiding the refresh times when I just for example do a tiny amendment on a column