The charge time will be related to the capacity of the battery which is quite large in these vehicles; you probably have a 90Ah battery. On a 12 amp charger, that would take about 8-9 hours to fully charge although it should start well before then.

As a general rule, you can measure the state of charge according to this (for AGM battery):
100% (fully charged) - 12.80+ volts
75% - 12.60 volts
50% - 12.30 volts
25% - 12.00 volts
0% (dead) - 11.80 volts

That would be measured at the battery itself after its been off the charger for a couple hours. It will read higher fresh off the charger.

https://www.energymatters.com.au/com...age-discharge/

If it still doesn't want to start after verifying the battery is charged, try connecting a jumper cable between the engine & ground point under the hood as a makeshift ground strap. If that still doesn't work, you can try connecting a battery pack or use the jumper cables to connect another battery to the jump post under the hood which would help rule out the fuses in the back of the X5. The jump post goes directly to the starter iirc.