Haven't looked at the source code of top, but it seems like 3019:57 in column TIME+ means 3019 minutes 57 seconds of accumulated CPU time.
999:00.00 means 999 minutes
1000:00 means a thousand minutes (no . separator at all)
I confirmed it on my system. I took an example process from top with 2529:38 then checked it with ps -fp PID which showed 1-18:09:38. The latter is one day and eighteen hours, which is approximately two and a half thousand minutes. Hence it equals the former.