"And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided."- (2:186)
"And your Lord says, "Call upon Me; I will respond to you." Indeed, those who disdain My worship will enter Hell [rendered] contemptible."- (40:60)
Allah has given no restriction nor any limitations upon the supplications we make but make the best duas to benefit you!
You can go through this blog to help you t allocate the best timing for your duas:
http://turntoislam.com/blog/371/best-times-to-make-dua-supplication/