Once you start using liquid yeasts you need to get used to long lag times, and a long lag time is NOT necessarily bad!!
You won't be pitching anywhere near as much yeast as with dry yeast. When you pitch a starter, the yeast spends time adjusting to your wort: its composition, gravity, temperature etc. It then starts budding while there is oxygen in your wort, while it is doing this it only creates tiny amounts of (metabolic by-product) gases. The more oxygen, the longer the budding process will take.
By consuming oxygen the yeasts are making life impossible for aerobic bacteria and lowering wort pH, so your beer is being protected even if you don't see any signs of life/airlock bubbling. And a huge amount of yeast is being generated. So, aeration is really important with liquid yeasts: shaking the fermenter does not cut it anymore.
You understand then that at the end of the budding phase all the yeast cells except the very latest generation have crater marks on the cell walls, and they cannot control the entry or egress of ions and molecules passing through the cratermarks. So for beers with OG>=1050 you should aerate again 14-18 hours after pitching (ideally) and the yeast use this second smaller burst of oxygen to generate sterols by which they repair their cellwalls. You now have plentyful and healthy yeast to ferment even the biggest beer in 5 days.
For more info, search on "Clayton Cone" in www.hbd.org archives.
If there is no airlock action or krausen (never trust an airlock!!!!) etc aerate the wort by dropping it into another fermenter a few feet below the full one.
Jovial Monk