Development of Model X has not hurt the timeline of Model 3. Model 3 could not have been produced earlier because battery prices have to come down more from where they are now (which comes from two elements: time and the Gigafactory). It would never have been possible to introduce Model 3 at a price of $35,000 for sale in 2015 or 2016. End of 2017 is and was the earliest possibility, regardless of what happened and happens before.
And the huge profits on Model X in the next 2 years will be paying for the investments necessary for further development of Model 3, for the Gigafactory needed for the batteries for Model 3, for the production capacity for Model 3, for extra superchargers for Model 3, for extra service centers for Model 3, etc, etc.