if you have a job then you can apply for loss of earnings - but i wouldent bother i dident its just hassle you could do without and at the end of the day youre there because you want to join the army. So im sure you could give them a couple of days for free.
Don't get paid to turn up to interviews in a civilian job do you?
Also; I think it costs them enough with train fares, food, etc. Especially when not everyone that attends passes. So in turn, that alone is dead money!