I am training to be a nail tech. They last 3-4 weeks before having infills or new nails. However they can come off for lots of different reasons, most likely how the technician puts them on, but also if you have diabetes or another illness or are taking medication, using your nails as tools, the quality of product that is applied to your nail, detergent you use (best to use gloves) also suncream, chemicals and sometimes lots of sun can cause them to yellow. Also if you take the polish off your acrylics only use non-acetone polish remover. And if for whatever reason you need them off DO NOT prise them off like I do even if its lifting off as it can cause serious nail damage. you can bye acetone from boots: pour enough into a bowl (not plastic unless its acetone friendly) and soak your fingers for 10-15 mins until the acrylic has soaked off.
Make sure you apply cuticle oil and hand lotion regularly after having acrylics or a removal done to moisturize your nails. If they chip or lift you should go to your nail tech. if you want to know anything else I will try and help.