If you look at the website https://vlb.io/#ico , you can see that the price is fixed through time, which is 1 ETH = 650 VLB, but each period gives different bonus. For this presale time they gives us 30% bonus, and later on the ICO (12 March 2018) they gives us 20% bonus, so the faster the investment is the better for a great project like this.
As far as i know, the minimum investment for someone who wants to join is at 0.5 ETH, because thats the amount the official wallet address got from the investor.