In the summer it really depends how long the ride is going to be – if i’m going down the supermarket i just go with what im wearing but i dont really class that as a “bike ride” its only 5 minutes each way. For an hours ride then a couple of minutes to get ready and fill a bottle but for a longer ride then will need to get food out and make a drink up, check the weather forecast see if i need to take a waterproof / gilet / arm warmers etc, have a quick check of the bike to make sure everything is good.
In the winter even a short ride will take a while to get ready for. If i organised my clothes more then it would be quicker but i am forever losing base layers, undergloves, overshoes (which when i eventually find take me about 5 minutes to get on properly because they are so tight!)
If you are going to be out for a few hours particularly in the winter then taking a bit of time to get properly prepared is worth it. For me it is the difference between feeling comfortable after 3 hours as opposed to feeling miserable after 30 minutes!