I believe that if there is a re-phasing/relaxing if current conditions, it will happen in August and we would see a second lockdown in Oct/Nov where "winters" are about to take root. Of course, the only real parameter would surely have to be systems being able to accommodate the sick. If we could get to a stage where enough ventilators exist to deal with the potential demand, that would likely be the single biggest factor in all this other than a vaccine or anti-body shot.
Here in Norway they've announced some relaxing of the restrictions towards the end of April. Child care and schools will open and businesses requiring one-on-one interaction such as hair dressers will be allowed to open as long as they implement certain measures (no idea what those are). A ban on large gatherings such as festivals will probably be in place for some time.
With the sun coming out and the weather getting warmer, there's no way people will be isolating themselves much longer. I drive to and from work every day and there's people everywhere, large groups as well. What's the point in having so many off work if they're just going to hang out with friends/family instead?
It seems the goal here is to keep the rate of infection low enough to avoid hospitals getting overwhelmed. Large scale testing to see how many has actually had it is definitely needed. Hopefully the virus will go away for the summer and the people in charge take that time to get everything in place for the next outbreak.