Expression for time in terms of G (universal gravitational constant), h (Planck constant), and c (speed of light) is proportional to:

F=GM²/R² ⇒G=[M⁻¹L³T⁻²]
E=hv ⇒h=[ML²T⁻¹]
C=[LT⁻¹]
t∝GˣhʸCᶻ
[T]=[M⁻¹L³T⁻²]ˣ[ML²T⁻¹]ʸ[LT⁻¹]ᶻ
[M⁰L⁰T¹]=[M⁻ˣ⁺ʸL³ˣ⁺²ʸ⁺ᶻT⁻²ˣ⁻ʸ⁻ᶻ]
On comparing the powers of M, L, T
-x+y=0 ⇒x=y
3x+2y+z=0 ⇒5x+z=0
-2x-y-z=1 ⇒-3x-z=1
On solving (i) and (ii)
x=y=1/2, z=-5/2
t∝√GhC⁻⁵