May/should one go to Mikveh if they are in quarantine?
Update (Rosh Chodesh Nissan): See here.
Women’s Mikvah:
A woman who is quarantine should not go to Mikvah. In addition, stay posted with the guidelines of your local Mikvah.
Men’s Mikvah:
A man who can not go to the Mikvah, can use tish’ah kabin of water – according to many opinions, this method can be achieved by taking a shower for several minutes (see further), while standing upright with your hands loosely by your heart (even if the water doesn’t reach all parts of the body). [For further reading on this, see here].
Many sources hold that tish’ah kabin suffices for tosefes tahara also.
The amount of time really depends of how much water comes from the shower head. it is approximately three (3) minutes. To ascertain exactly how many minutes are necessary, one can put a pail where it can catch the water to measure how long it takes for the water to reach the required shiur (approx. 12-16 liters).
A bath can also be used.
Another option (for Tosefes Tahara only) would be to learn a perek of Mishnayos in Maseches Mikvaos.
Do the 3 minutes start דוקא from when you turn on the water? Or can the shower be running for as long as you want before you go under for 9 kabin?
No. Three minutes – or more or less depending on your shower head – is the amount of time you need to be under the water
Regardless shower shouldn’t be turned on till your there so it be considered כח גברא.