Viable if you are US citizens/residents, tight otherwise. Train between terminals is 5 min and reliable, so only issue is time it takes to clear immigration and customs and whether EK arrives on-time (you can check their arrival stats). Jetblue did have some infamous hour-long check-in lines a few years ago but haven't heard of that recently, so check-in/secuirty shouldn't be a big problem, but flying an LCC does mean it will take longer than most other airlines.