A custom gizmo combining Nuke's native Text2 node with an animatable, frame-driven countdown / count-up value.
Set a Countdown Start/End Frame and Start/End Count, choose an interpolation curve, and the displayed number ramps automatically between them. Use 'Bake to Keyframes' to convert the live ramp into real, hand-editable keyframes you can override at any frame.
All standard Text2 controls -- font, size, justification, box, and mask -- are exposed on the Text and General tabs.
Tested in nuke 16 and 17. Its all standard knob controls, so it should work with other versions. Please let me know if if not working on a specific build.