Neptune's years are 164.8 Earth years. Its days are 16 hours and 6.7 minutes long. Although Neptune's days are shorter than our days, its years are still longer than ours.
Most colorants will last in your pond approximately 30 days. You may have to add more pond dye before 30 days if you have execissive rainfall, run-off, a heavy out flow, or evaporation. If your colorant is fading you will visually be able to tell and should add more dye to the water.
Though some people prefer to wait as long as two to three months between reapplying hair dye, a period of six to eight weeks is sufficient enough to reapply hair dye. Permanent colouring dyes contain a greater quantity of Ammonia and Peroxide where as temporary hair dyes contain either none or negligible quantities.