I do 5 minutes of dumbells everynight before bed will this surely but slowly build up some decent muscle, or is it too little to even make a differance?
If you want to build muscle, it's more useful to think in terms of reps and weight than time spent per session.
The idea of strengthening or building a muscle is based on progressive overload, i.e. increasing the weight or number of reps performed over time.
People bang on about good form because it's the only way to regularly perform these movements long enough to see changes without doing yourself an injury.
Similarly, while dumbbells are a good place to start, you'll probably find them too easy very quickly and will eventually have to pick up a barbell, so that you can load it with enough weight to keep progressing.
It depends what you want to achieve, but for general health and fitness there's nothing wrong with calisthenics and 30 minutes of cardio a day. You can do a calisthenic routine of stretches, press-ups, crunches, squats, etc, without paying for any equipment, you get a whole body work out, and rather than increase the weight you can just do more reps per set, or more sets over a longer period of time. It's good for endurance and stamina, but no so much for building huge muscle mass - but whenever you start any exercise, if you're eating well you'll get good 'beginners gains' and reach a noticeable improvement fairly quickly.
