This time it took the 35-year-old right-hander four days to reach the milestone.
He started on Monday and finally brought up his 20th first-class hundred for the province - his third this summer and his 22nd in total - during the morning session yesterday, and just in the nick of time.
He forced a delivery from Canterbury pace bowler Matt Henry through the covers for a couple of runs, much to the relief of some of his nervous team-mates - probably none more so than No 11 Craig Smith.
Smith had joined Cumming at the wicket when he was on 99 and had to survive two deliveries from fast bowler Richard Sherlock.
The 100, though, was a small consolation for Cumming.
The game was ruined by poor weather and both sides had to be content playing for first innings points with so much time lost.
Dean Brownlie scored a patient half-century to help Canterbury overhaul Otago's first innings tally of 199 with five wickets in hand.
"We wanted to pick up points and it was disappointing to play for just two points," Cumming said.
"But it was an interesting 100. I had to deal with stopping and starting and pitch conditions, which were tough. We were four for not many as well, so from that perspective it is nice to dig in and show a bit of patience."
Cumming was the last man standing and in 83 first-class games for the province it was the first time he had carried his bat.
"With our top order it is pretty hard to do, because you normally have someone doing well. I've been the last man out before, but that was the first time."
While Otago (22 points) was disappointed not to pick up any points, its main rivals were unable to stretch their lead significantly.
Only 8.2 overs were possible in the match between competition leader Central Districts (29 points) and second-placed Northern Districts (27pts) in Napier.
With no result possible on the first innings each team was awarded a point.
Wellington (25 points) was the big winner.
It achieved an outright victory against Auckland and picked up the maximum eight points, to move into a share of third place with Canterbury.
Former international strike bowler Mark Gillespie (four for 44) and speedster Andy McKay (three for 30) combined to help dismiss Auckland for 144 and claim a 126-run victory.
With two rounds remaining only seven points separate the top five sides.
Only Auckland, on eight points, is out of the running.
"All the teams will be under pressure and that pressure brings out different traits. One of the good things about our team is when we've been under pressure in the past we've played well," Cumming said.
Otago plays Northern Districts in Hamilton next week with Auckland hosting Canterbury and Wellington playing Central Districts at the Basin Reserve.
