It is not lawful for you to offer salah while sitting by gesture in the light of the question mentioned above. Your salah shall not be valid. You should demand the authority to allot you time for offering salah otherwise join any other coaching centre where you may get the facility of offering salah. Or choose such a time for your coaching that the times of any salah does not fall in between. In short, it shall not be lawful for you to miss fardh salah for coaching according to Shariah.
Allah knows Best!
Darul Uloom Deoband