1. You need to ask the insurance exactly what is needed. Eg, for AIA it is their form which the doctor needs to fill up plus proof. Most of the time the proof or supporting documents should be available when they discharge your father.
2. Did you apply through formal channel? If so typically it takes more time. If it is like the above example to fill up the form, you can try to make appointment with the doctor and ask him to fill up on the spot. Normally the nurse will do it and he will just sign off. Then again this depends on the doctor, you have to pay of course for the doctor appointment plus any other hospital related costs.

Good luck to your father and your claim. My advice is to contact your insurance agent or be more dilligent to read the fine prints. ie exactly what is needed from the doctor to ensure the claim is successful. You don't want a situation where after you pay the money and spent the time to get the "report" only for the insurance company to reject base on whatever excuse or reasons they can find.