Yeasts can take longer than 24 hours to show signs of fermentation, especially if you didn't make a starter. The lag time between pitching and the start of fermentation is when the yeast reproduce and increase their population to a size that is big enough to consume all of the sugars in the wort. So if they are starting with a lower population then they should have, it will take them longer to multiply to the right population. You basically just used a mixture of the two yeasts so you will get a mixture of Belgian and English characteristics. I'm sure it will taste just fine, but maybe not as Belgiany as you might have hoped.
Suggestions for next time:
1. Make a starter when using liquid yeast according to this calculator: http://www.mrmalty.com/calc/calc.html
. This will decrease the lag time and won't stress the yeast and cause them to produce off flavors due to under-pitching.
2. Be patient and wait at least 36-48 hours before you start worrying about your beer not fermenting.