'Since' as conjunction

if I use the word 'since' as a conjunction. i.e. 'Because'

Is it correct if I use future tense after 'since'?
e.g.:
I cannot join the event since I will attend a training course tomorrow night.

I found most examples in dictionary, all cases use pass tense after the word 'since'.
e.g.
At first he denied but since he confessed.
(but for this case, the word 'since' is used for adverb.)

My question is that: For a conjunction usage, is it possible to use future tense in the sentence with 'since'?

Thanks for your help and explaination.