I posted this before, but to my knowledge, the timeline was something like this:
-Nicko becomes significantly unhappy with the performances of Blaze during VXI tour. Goes to Rod and lets his feelings be known to him. (Possibly even threatens to leave the band) Rod tells Nicko to bloody get on with it and that they will deal with this matter after the tour.
-I think Bruce was happy with his solo career at this point. But there might be something there. Roy Z was absent during TCW tour, because of the combination of pursuing his producing career and personal issues. Despite Bruce saying that Guru was a good stand-in for Z, I still think Roy was much better, judging from bootlegs. I think Bruce was a bit displeased by this and this could be one of the factors why he wanted to ditch his solo career, since his main creative partner wasn't fully commited and somewhat unreliable.
-November 1998: The VXI tour is coming to an end. Rod comes to Steve and tells him about Nicko coming to him mid-tour. Steve agrees that they replace Blaze, but is reluctant to ask Bruce back. It takes a lot of time and persuading from Rod for Steve to give him a go-ahead to call Bruce. But in the end he does. I think this could've taken a whole month, but I doubt they auditioned any singers during that time, but they had some people in mind if they couldn't make a deal with Bruce.
-Early-Mid December 1998: Rod contacts Bruce. Bruce is on the fence what to do. Paddy and Roy get Bruce drunk, heavily persuade him and make sure that one of his demands is that they take H back too. Bruce is probably pretty scared about going back to a band with Steve at the helm of everything and him having basically no say, after a solo career, where he basically did whatever he wanted. This is the point where probably Roy suggested that one of Bruce's demands is an external producer (hoping that was him, but I think in this case Steve was a bit afraid that will give power to Bruce, so Caveman was hired). Bruce agrees to rejoin, if his solo band is cool with it. And then comes the infamous Casillas line: World needs Iron Maiden.
-Late December 1998: The meeting between Steve and Bruce is arranged after new year's.
-Early January 1999: Bruce and Steve meet up and they are cool with eachother's demands and the future direction of Iron Maiden. Blaze is informed that his services will no longer be required.
-February 1999: Bruce and H are officially back.
So, IMO, Bruce rejoined in January 1999 and no other singers were auditioned.