For the purposes of this question please include research from the Monero Research Labs and any time preparing the work that is visible in GitHub today.
Itemization of estimated hours for each focus (RingCT, LMDB, Kovri, GUI, etc) would be ideal but is not necessary.
This is really hard to tell, but here are a few things we know:
In April of 2015 smooth estimated that there was a rough estimate of two to three full time equivalents working on Monero software development, testing, and research reports. For clarity, this estimate varies over time.
moneromooo spent at least 710 hours (https://forum.getmonero.org/9/work-in-progress/2410/a-continuation-for-all-purpose-programming-of-what-needs-to-get-done-in-monero, https://forum.getmonero.org/22/completed-tasks/334/fund-a-developer-moneromoo-will-work-part-time-on-monero-for-260-hours-over-approx-6-months)
Ilya spent some amount of 280 hours on the GUI (https://forum.getmonero.org/9/work-in-progress/2476/the-official-qt-gui-project), there is some item list in the thread.
other tasks in that forum may or may not mention smaller chunks of time.
This is start to give an idea maybe, but I doubt it can be made into a reasonably accurate estimation.
