What is your definition of "activity?" If you mean airlock then all that more than likely was happening was that you were venting some of the O2 from oxygenating the wort.
One thing to remember, fermentation can take up to 72 hours for the yeasties to start, it's called lag time.
https://www.homebrewtalk.com/f39/fermentation-can-take-24-72-hrs-show-visible-signs-43635/
Especially since you didn't make a starter for your liquid yeast.
unless you are making a beer with an og of 1.020, you really need to make a starter with liquid yeast.
If you look at the pitch rate calculator at Mr malty
http://www.mrmalty.com/calc/calc.html you will see that there is only enough cells in a liquid yeast tube or smack pack for a very low gravity beer.
Liquid yeast, regardless of where it comes from, a tube, a smack pack, a slant, the dregs of a couple of bottle conditioned beers, OR that mason jar at the back of your fridge from a year ago, Should have a starter made REGARDLESS of the og of the beer. Yes Mr Malty says that for beers at 1.020 and below you have plenty of yeast, i
f you make a starter you'll have peace of mind.
And you won't be starting an "is my yeast dead" thread in a couple of days.
Making a starter first insures that your yeast is still alive and viable before you dump it in your beer. You will be less likely to start one of those "is my yeast dead?" threads that are on here every day.
You will also ensure that you have enough yeast usually the tubes and smack packs are a lot less yeast that you really should use for healthy fermentation.
Making a starter also usually means your beer will take off sooner, because the first thing that the little buggers do in the presence of wort (whether in a flask or in a fermenter) is have an orgy to reproduce enough cells to do the job...So it won't take such a long time in the fermenter since they started doing it in the flask.
Additionally it is better for the yeast to consume and reproduce incrementally rather than just dumping them into the fermenter...The yeast will be less stressed out than if you just dump them in.
Stressed out yeast can lead to a lot of off flavors...maybe even (though rare) the dreaded autolysis....Or the curse of 1.030....getting a stuck fermentation because the yeast have bit the dust.
So making a starter proves your yeast is still healthy, allows you to grow enough yeast to do the job, cuts down on lag time, and ensures that you will not get off flavors or stuck ferementations from stressed out yeast.
So give it 72 hours then take a hydro reading....but until then relax, it will be fine.