The test flight which lasted about 2 hours is the final items that needed by the FAA in order for order for them to certify the battery fix. In the next few days Boeing will turn over all the remaining data that is needed. The FAA and Boeing will have a continuous dialogue over the next few weeks and the FAA may even require more tests before giving its approval but the general consensus is that the FAA will give its approval to the fix and approve of Boeing's Service Bulletin & amend the emergency Airworthiness Directive it issued in mid January grounding the 787. Boeing has teams in place to start implementing the fix once the FAA (and other international aviation regulators like Japan's JCAB and Europe's EASA) have approved.
The fix will take 4 to 5 days to install on each aircraft though I think it's reasonable to assume that multiple aircraft will be worked on at the same time. Assuming that Boeing has (according to reports in the media) 8 teams ready to implement the fix along with the associated hardware at the ready, it will take Boeing about 6 weeks to return all 50 delivered 787s to service. If the approval is given by middle of April then it is reasonable to assume that the 50 787s that are grounded can resume regular revenue service by early June depending on the individual airline's readiness to do so.
So how long until deliveries begin? Boeing will have 30+ 787s ready for delivery but waiting for the battery fix to be installed. I don't have any information as to how many of these service ready 787s can be modified each week but I think it is reasonable to assume that Boeing can have up to 3 ready each week to continue the standard pre delivery ground and flight test regimen once the FAA has given its approval. I am also assuming that Boeing will start ground and flight tests from scratch given the new equipment that is being installed would also need to be tested out on each aircraft. Thus I'm assuming about 5 weeks for all pre-delivery ground and flight tests to be conducted prior to delivery. This would translate to roughly 6 weeks before Boeing resumes regular 787 deliveries. This would mean that deliveries can resume as early as the beginning of June. It still uncertain how many 787s Boeing can deliver this year until deliveries actually re-start and the rate of battery modifications are determined but at the moment they're maintaining their 787 delivery guidance at 60+. It is still possible to reach that goal but it would mean that Boeing will have to undertake an aggressive rate of production testing on the 30+ 787s that are on the lines at Everett and Charleston.
An added complication are the NTSB hearings scheduled for the second half of April concerning the lithium ion battery technology as well as the FAA's certification of the 787's battery system along with Senate hearings into the FAA approval process for the 787. While I don't expect any earth shattering news out of any of these three hearings pundits wondered aloud if these hearings will have any bearing on the timing of FAA approval, with some saying that the FAA won't give its approval until after the hearings are done. Transportation Secretary Ray LaHood even said that the fix that Boeing has proposed appears to be good. Whenever the FAA gives its decision, it does appear that Boeing in on the verge of overcoming yet another issue related to the Dreamliner.