Dont think of it as 5 years think of it as 60 months.
As to how many tasks constitute a year of experience that is subjective. But its not difficult to give yourself a ball park idea is it.
365 days in a year working 4 on 4 off equals round it down to 180 now knock off some leave and sickness as we do, say 30 - 35 days would give you approx 150- 145 days where you could record tasks. Simples.
Just a guideline thought if you are struggling