Most experts are saying 30-50 years.

One problem is that making hydrogen is less efficient than simply using the electricity to power cars in the first place. Something like 85% vs 25%. The other problem is infrastructure which largely already exists for electric vehicles.

Plug-in hybrids and all electric vehicles are the only realistic short term solution. All that's really missing are affordable high capacity batteries.

What the fuel cell now is doing is taking the place of those future batteries at the cost of efficiency and subject to the limitations of fuel station availability.