XF 1.4 Error 500 during "Complete Import..." step

While importing data from phpbb 3.0, a server 500 error occurred at the last step (Complete Import...). Unfortunately, I am not aware of the exact stage of the process at which this happened, but I know it was sometime AFTER the rebuilding of the user caches took place. The server error log shows the following:

[warn] mod_fcgid: read data timeout in 40 seconds
[error] [client xx.xx.xx.xx] Premature end of script headers: admin.php, referer: http://FORUM_URL.XX/admin.php?tools/run-deferred

I tried reloading the page and it took me to the backend's homepage with no message whatsoever.

How can I manually execute the "Complete Import" step? Is it OK to just rebuild all the caches at this point?
I went and did that without waiting for your answer since we had enough downtime as it was. We are running XenForo for almost 10 days now with no problems whatsoever.

Just to add that I am blown away by your product, great work.