How long does it take for a geyser to form

Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets rock heated by magma. The geothermally heated water then rises back toward the surface by convection through porous and fractured rocks.

50-100 minutes

Explanation:

The process begins again. In some small geysers, the eruption process can take just a few minutes. In larger geysers, it can take days. The most famous geyser in the United States, Yellowstone National Park's Old Faithful, erupts about every 50-100 minutes.