Prepare a detailed return-to-work plan in partnership with your employee. Document it, stick to your part of the bargain and monitor it.
The sooner some form of return to work can be discussed and implemented, the better. This does not have be a return to full hours or even full duties. There are a whole range of options for a phased return to work.
When collaborating on the return-to-work plan with your employee, make sure you document it in detail and agree when and how it will be reviewed -- the likelihood is that it will need to be adapted over time to ensure it continues to be fit for purpose.
There is no standard period for a phased return to work. It could be over a few days, weeks or even months, depending on the nature of the situation. You can tailor something that works for both your employee and your business. The key thing is getting your employee back to some form of work at the earliest opportunity and building from there. Having a plan will help with sustaining the return to work.