Between 18-25 weeks most moms will be able to feel fetal movements. The American Congress of Obstetrics and Gynecology (ACOG) recommends that you measure how long it takes to feel 10 kicks, flutters, rolls or swishes. Usually you will feel these movements within a 2 hour period. Most times it is sooner than that.
If you are not feeling an adequate amount of movement then it is recommended that you call your provider right away.