No, going when you can't see space for you on the other side is
needlessly blocking the junction. If traffic is stop-start, as it
would be in such a situation, sending one car over the junction at a
time is the only way to ensure the junction is not blocked, as
blocking the junction screws up everyone else. When driving you
can't assume anything.

Obviously when traffic is stop-start you don't enter the box junction until
you can leave it. But if traffic moving at full speed across box junctions
refused to enter until their exit was clear, the capacity of the road
network would be slashed, and gridlock would result, the very thing that box
junctions are supposed to prevent.