I agree with BlackFatalii,
No need after germinating. HOWEVER, depending on what climate you are in, and what the temperature is of where you are starting you seeds, leaving the heat mat on MAY help speed up the growth rate on young seedlings.
Plants love warm ground... not hot... warm. This is how Mother Nature brings seeds to life in the wild.. with a warm ground, rain and sunshine. All we are trying to do is replicate what God does outside...inside.
As for me, I start 600 seeds per year... that is way to many warming mats so I use a grow tent and a 1000w hps lamp... the lamp produces heat and that, keeps the seeds warm. Some say don't use such a high power lamp for seedlings.... but, the sun outside doesn't dim for new seedlings... Why should the lamp...
Using a covered seed flat.with a heated map. Not grow lights turns on yet... currently in a south facing window in san fernando valet.
If half the seeds germinate, should i move that half out while waiting for the rest? Or maintain until all germinate? The ones i considered to move do not have true leaves yet.
many thanks. yearly container gardener but first time with seed start !