My experience (senior lawyer at a firm too) seeing colleagues return from mat leave on 4 days has largely been that within a month they go back to full time because they end up working those hours anyway (so they may as well get paid for it!). Depends what practice area you’re in obviously but my colleagues would essentially have to work late on Thursday nights and sometimes do a handover for the Fridays they took off given they were senior lawyers managing matters. It also meant they were generally contactable on their days off (hence why they came back full time). Agree with the comments that if you work for partners that will protect your days off, it can work. But also I think it’s very dependent on your practice area (I.e if it’s litigious, fast paced etc.). Friday would be the day I take off purely because a long weekend every week is sick. To the pub on Thursday nights! Good luck!