So how do you intend to pressurized the vessel? directly,in line, from either a centrifugal, rotary or reciprocal compressor or from an air line supplying air at constant pressure? lots of variables to consider in you OP.
I feel there is no right answer to this question as there are too many variables.
Is this a one off or unusual occurrence or does it happen several times a day?
Have you any issues with low temperatures . hydrates , condensation going from 65 bar to 1 or 2 bar at the start?
Is there a capacity restraint on the supply line or regulator??
what is the relative size between vessel size and inlet pipe size?
how much time have you got?
Will you be loosing money the longer it takes to fill the vessel?
Most people would say avoid shock loading, but otherwise you could have an answer anywhere from 10 seconds to 10 minutes. Your call.
Normally it's a compromise between the mass of gas required and the size / cost of the inlet pipe and regulator and any temperature issues due to J-T cooling.
Sometimes you need to start slow to avoid cooling the vessel too much and then speed up, but if it's a small vessel compared to the inlet flow rate then this may be over so fast that there is no cooling.
So think about the issues above then run a few scenarios / costs etc and present them to whoever is paying the bill and let them decide what their drivers are for the pressurisation rate.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
If you Google Compressed Air Tank Calculations you will find lots of information on information and equations on how long it takes to pressurize a vessel to a given pressure.
Things you will need to know:
Volume of receiver
Starting / ending pressures
volumetric flow rate of gas/air
With those equations from the likes of Engineering Toolbox you should be able to work what you need.
Equation (V)(P2-P1)= (14.7)(t)(Q); whereby V (cu.ft) is tank volume; P2 (lbf/sq.in.)is final air pressure in tank; P1 (lbf/sq.in) is initial air pressure in tank which could be atmospheric pressure if tank is empty; t(minutes) is the time required between P1 to P2; 14.7 is the atmospheric pressure in lbf/sq.in.; Q (scfm)* is the standard air flow rate in cu.ft./min.. Manipulate the equation to (P2-P1)/(t) to answer your OP. This equation is assuming constant temperature which is reasonable if the tank is large enough or if the time to pressurization is short under a slow flow rate so that the heat of compression is dissipated. *scfm is the standard air flow (cu.ft./min.) that the air line (per your OP your supply source) would deliver at either:1) temperature of 68dF at 14.7psia & 36% R.H. per ASME. 2) 70dF and 14 psia per compressed air institute. 3) 14.4 psia and suction temperature per the natural Gas Pipe Field. Reference: Plant Engineering (1970's article), Directory & Specification catalog; Air Distribution. In association with this article is a nomagraph. On your part you'll need to determine the scfm from you supply source (air line to the tank) which will require testing of the air flow and its corresponding pressure. There is also data on the amount of free air(at scfm) delivered by different pipe sizes; if I find the data in my archive I'll let you know.
A thought on determining an approximate scfm is to use the sonic or sub sonic rate of air flow equations depending on the initial pressure of the tank.
