I have not been a contestant on anything like the Sewing Bee but have been an extra in loads of productions and yes, filming takes FOREVER and days are looooong.
Fairly typical to be called to arrive at 7am, sign in, have a coffee, hair and make up, wardrobe take photos to make sure you look the same all through the day, bacon roll, hang about, bus to filming location, hang about while techies dicuss lighting and how to shoot the scene, extras placed into scene and stand around for another 45 minutes while lengthy discussions with directors, one rehearsal, more lengthy discussions, then it's lunchtime and everyone downs tools for 90 minutes, then checks again by wardrobe to make sure you've not spilled lunch all down yourself, then back into position, more hanging around, another rehearsal or three, director changes their mind and moves peoplre about or changes what you're doing, another rehearsal or three, then finally a take, more discussions, couple more takes, director calls wrap after getting approx 20 seconds in the can, back on the bus, another coffee, sign out. By which time it's about 8pm. No exaggeration.