Examples of organisations who have institutionalised volunteer leave:
Singapore Pools: A corporate culture of giving and doing good, Life & Culture - THE BUSINESS TIMES
DBS, Keppel Corp, Salesforce, Standard Chartered Bank, UOB: 'Keep the good going': Companies that give employees time to volunteer - CNA (channelnewsasia.com)
Johnson & Johnson launched two-day volunteer leave in 2021: https://www.linkedin.com/posts/alice-chiu-2b85bb3_how-social-engagement-can-put-a-smile-on-activity-6807602403689459712-WT0V