Index Fund Investing Philosophy - Cost Averaging vs Lump Sum Hi,

I have recently opened up a TFSA with Tangerine (Balanced Growth) in an attempt to save for retirement using the couch potato strategy. I have setup an automatic withdrawal of $50/biweekly. With my job, I can frequently make more money working overtime. This year, I will have made ~$15,000 more than my base salary. With that being said, I was wondering if it would be smarter to increase my biweekly withdrawals, or wait till the market is cheaper to buy more units (potential market crash).

Thoughts? 