Heat element(spring) does not stay on lon...

you found the problem yourself, yes its a thermostat, replace this, however the heat should stop on longer than it does,

but please note this is a part that should cut out & reset itself, if needed to prevent fire or overheating, this part has gone what we call tired,

do not bypass anything on the appliance and use it, this can be dangerous and is against health and safety law etc

before continuing to use the dryer check all pipes for blockages as restriction of air flow causes the problem you have, so to prevent another faulty thermostat clean out properly.....