Definitely not very long dear. Probably an hour or so... If u use high end strightner with hair protection spray it will stay for long hours or until u wash ur hair
I usually have lot of hair fall, since I do not care much and lack of deficiency. It will not be the same for everyone, of course if u do it on a regular basis ur hair will break and lose its shine.
Generally not advisable to use anykind of heating tools daily,.since ur hair might loose it's shine and strength. More sure to take good care of ur hair such as oiling, applying hair mask, using good heat protectant spray if u are using these kid of heating tools in a daily basis.