One way viva processes differ around the UK is in terms of awards. These are the various outcomes. Often people think in terms of corrections: no corrections, minor corrections and major corrections. If your viva is coming up I would encourage you to check exactly what each of these means at your institution.
Some universities give three months for minor corrections; others, only four weeks. At some institutions major corrections is an acknowledgement that your thesis is on track but you have some substantial editing or rewriting to do; at others, you must formally resubmit your thesis and have a second viva. Check the outcomes before you go to the viva. Better to know all of the possibilities…
…and then temper them with facts. Most people get minor corrections. It’s likely you will too. They won’t be terrible, but they’ll still be work that needs doing. Sketch a plan now. How long would you have to complete them? What would you have to do in order to complete them in that timeframe given everything else you have going on?
Be realistic. Prepare to pass and prepare for that final burst of work to make your best thesis.