Approximate mining periods of 30 to 60 minutes unlock rewards which are distributed according to a changing growth plan.
Helium explains that at the start, node owners will accrue more HNT for building out network infrastructure, while later on, it will be more advantageous to transfer device data. This adjustment mechanism for token distribution is expected to last for around 20 years.
As of the start of October 2020, there are 48,712,218 HNT in circulation. When the token launched, the supply was zero, with no premine.