If I do the same thing every night, will it become less effective?!

i agree same muscle group not gonna be to good for yah. mix it up
but try it. if it isn't effective try something new :)
you can make a 15-20 minute routine to do every morning or evening if can really be bothered haha
or 3 times a week
or weekdays
up to what you think you will want to stick to, then just set the times and days and stick to that
but not just dips
try squats and some pilates and yoga moves
bit of meditation after in the morning always helps me actually willing to do it again the next day because then its your mind and body as one .. better motivation that some guilt trip have to haha :)

You shouldn't be working the same muscle ground every day in the first place. Put a t least a day in between so your muscle can actually rest