Photos taken by different devices not effectively sorted by time
During my holidays I took pictures with my iPhone and with an old Nikon D60 camera. I synced iPhone photos via iCloud and imported the Nikon photos to Apple Photos. I would like to merge the "two sources" simply by time. In Photos I selected View->Sort->Keep Sorted By Oldest First, but still my pictures are not exactly merged. They generally are, but seems that they stay a bit grouped by source device and it happens that some photos taken by one device on a moment are sorted after photos taken 2/3 days later by the other device.
Can anyone help me on that please?
thanks in advance
MacBook Pro 13", macOS 10.15