...Would you describe your understanding of the big bang (in regards to the creation of time) as an assumption or an empirical observation?
Neither and both. Certainly there is the basics assumption of science: The universe is acting as if following some static laws of nature. Certainly it is based on a great deal of both astronomical and nuclear physics experimental results. (It always seemed interesting to be that the two extremes of scale are so closely tied together in the physics of cosmology.); However the big bang is a mathematical effort to efficient model much of this information in an elegant and self-consistent way. Very much like the origins of science in pre-Christian astronomy - there were millions of observations and they were consolidated in a epicycle model which worked well when tested for example predicting eclipse some years in advance. Maxwell made one of the most important unifications, but the standard model is also one, not yet finished as gravity just does not seem to fit.
This need to model and consolidate many facts has been the mother of both physics and applied math. Physicists often lead the way in math as they are not so concerned with mathematical rigor. \For example the Dirac delta function was in wide use by physicists, while mathematicians were still struggling to find some way to make it rigorous enough to use in their field.
... as a general rule, god tends to be guided by magnanimity rather than necessity ...
Welcome to my "Multi-Gods" Club. It is an ancient POV - most all have held it in the past, before those trouble making Jews ASSUMED there was only one God. (Clearly false idea and the hurricane and flood gods are growing angry about this now, it seems.) If there were just one god it would be a single case, not a "general rule." Again welcome to the MGC.
...you can't see how you have the same problem with the big bang creating time?
No, not really, for several reasons.
(1) I do not think time exists, and have defended this POV in several threads. Mathematically by solving (in principle) all the N equations of physics for "t" parameter that is used in them and setting all N equal to teach other (as they all equal "t") top re-form the equations of physics free of the convenient parameter "t". New set of N-1 equations describes all of physics and makes no reference to time. For example Earth's progress around the sun is directly related to the nunber pof 360 truns Earth has made. (there are lots of complexities and need to define indices and arbitrary origins of coordinate systems but this is nothing new. For example zero "right ascension" of astronomy is an arbitrary point and 2008 is and arbitrary index for actions that are periodic.
(2) "Time" is, like 3D coordinates (x, y, z) just part of the descriptive model called the big bang. Others in that model are the mass of a proton, the speed of light, the charge of the electron, pi, e, etc. All models have some "axiomatic set" of terms. They really do not state reality is as the model describes (that is the job of the religious or the philosophers, not the physicist) All the big bang does is to consolidate many observations in to a structured model, but it has been done after I grew too old to struggle with the details so I do not know the full model.
Saying: "God made the universe" is not a model that consolidates observations. God has not been observed by anyone alive today to do anything. In fact, the attributes ascribed to him by Christians seem very inconsistent with many observations like the black plague or Hitler’s Nazis etc. To avoid facing these inconsistencies, Christians can only say: "God works in mysterious ways." Yes the millions of children God has claimed as his own before they could walk or talk (in the black plague and Nazi Germany, or Africa today) is a mystery a "loving God" makes.
I will not comment on rest of your post in part because I doubt humans really have free will - Sure seems that way, so I was glad to discover a way it could be real (Consistent with physic/chemistry controlling the firing of all nerves in the body etc.) I have long post about this. Ask and I will dig up the link again. (Human evil is only possible if human free will is real.)