Regarding the Twitter connector, which tables are you referring too? Unfortunately the Twitter Search API only lets you go back up to a maximum of a week or 1500 Tweets so if this is what you are trying to use I am not sure how useful a start/end date would be. If you can provide more detail it would help.
Regarding Facebook - I am assuming you mean the Facebook Fan Pages Connector? You are right there is no start/end date possibility yet on start date until present. However this is on our road map as the Facebook API would support this - please DM me if you would like early access to test this.
Regarding your issue storing historical data - could you explain this in more detail please? You can use the standard QlikView QVD method to store hostorical data and we have Facebook and Twitter demo applications which show this in detail but perhaps I am not understanding your quesion.
A minor update to my last point - the Twitter search API does allow you to supply an 'until' date so it only returns Tweets before that we are not currently exposing this in the Connector though and you would still be limited to a maximum of 1500 or a week's worth of Tweets and it doesn't seem that you can specify a since date.
So I am not sure how useful this would be - if you could DM me or explain more about what you are trying to achieve we will do our best to add this functionality in.