1) History suggests you are most likely better off by investing as soon as possible. No guarantees this time, or any time.
2) Second option is unlikely to beat #1 (as suggested by many who have studied this exact question historically), however, it may help put your fears at ease. Invest 5k/month until it's all out there... or some other amount. If the market tanks, and you feel alright about it, then you can accelerate the purchases. If the market goes up, then you should feel stupid about not doing #1, and can learn your lesson.