30 mins should be more than enough. My line with the 7530 syncs within a few minutes.
I understand that you don't want to flash your 7530 right away, but in the end this device is way more capable and should be able to support your >100MBit/s line. As mentioned, keep in mind that you need to build your own firmware for this to work - see Adding support for VRX518 (and maybe VRX320) for details, I'm using the following fork with great success: https://github.com/dhewg/openwrt/tree/vr11