This question depends on how much you use the app... a crew that clocks in 10-20 times a day (like a maintenance crew) is going to use more data than an install crew, that might only clock in/out twice a day.
On average, LMN Time uses between 30-50MB per month, per crew. That's about 3-5% of your average phone data plan (based on 1GB/month data, per phone).
Other factors that may cause data usage to be higher include:
- Downloading job files
- Taking frequent timesheet photos (** note that photos are compressed to less than 10% of their original size for easy uploading/viewing)