Do I have to give all my spare time?
You do 19 or 27 training days each year, depending on your unit (national units 19 days, local units 27 days). If you do all of these days and pass the Military Annual Training Tests, you'll get a tax-free bonus payment on top of your pay.
You can do more training if you like - you're paid for each day you do so it's a good way to earn extra cash.
The great thing is that you can fit most of your training around your day job. You do it in the evenings and at weekends. There's also a two-week training camp each year. Apart from the camp, it's up to you and your unit to decide how much training you do.
If you're deployed on operations you will be away from home, and will need to take time off work. It is easy for you and your employer to arrange this.