Hearts lost 1-0 after an insipid performance that was in stark contrast to the drama which saw him appointed barely two hours after Csaba Laszlo's sacking.
"You've got to put things into perspective," he said.
"I've come in last night having not seen the team.
"I spent most of the time talking to the backroom staff who have worked here, saying, 'Does this boy do this? Is he good at that? Can he play here? Can he play there?
"We've had to patch up a side with so many injuries."
He added: "It was great to find out about boys I've never even heard of.
"There were two or three involved today.
"I've got to be the judge of whether they're good enough or not."
Despite losing by a single goal, Hearts were well beaten, with Saints wasting numerous chances to add to Kenny Deuchar's first SPL strike for almost two years.
Yet, Jefferies' side could have snatched a draw with the last kick of the game when substitute Gordon Smith's effort was blocked on the line.
"I learned a hell of a lot in 90 minutes today," Jefferies said.
"If we'd played from the start like we did in the last 20 minutes, where we got them on the back foot a wee bit more..."
Jefferies confirmed he wants to sign a striker before the transfer window closes on Monday.
"I've had brief discussions about that and I think we'll try," he said.
"They've got to be available."
Echoing the kind of talk that cost Laszlo his job, he added: "I certainly think we need another striker because you can't play the young boys all the time."
Jefferies played down suggestions Kevin Kyle could rejoin his former Kilmarnock boss before the end of the season.
"The fact that Kevin's out of contract and I brought him there, he's the obvious one," he said.
"Kevin's not going to be available before Monday because, by all accounts, he's committed to the club until the end of the season."
Jefferies admitted defender Jose Goncalves was left out of the side today because he may leave before the window closes.
He added: "The club want him to stay; I want him to stay."
The Hearts boss also praised Billy Brown and Gary Locke for assisting him at McDiarmid Park before the club had even decided whether to employ them.
And he had a word of warning for captain Michael Stewart, who had to be restrained as he left the field after taking umbrage at a late challenge.
"You've got to bite your tongue at times - Michael's been a wee bit guilty of not doing that," he said.
Jefferies insisted defeat had not diminished his enthusiasm for returning to the club he supported and captained before taking the manager's job between 1995-2000.
"I remember coming out of the meeting last night and three cars on George Street stopped and people jumped out because they recognised me," he said.
"I didn't get to bed until about two o'clock this morning.
"I've just been answering texts and phone calls."
Saints boss Derek McInnes admitted Friday night's news had affected his side's preparations for the game.
"We knew how the previous manager liked to set up and we had to try to guess that," he said.
"But we thought Jim might have come in and made one or two changes to it.
"We spoke about possibly Hearts being here in bigger numbers in terms of their crowd and that they'd get a lift."
McInnes was relieved to hold onto all three points but insisted his side were well worth their win.
"I thought we were very comfortable throughout the game," he said.
"You're always concerned when you don't get that second goal.
"I thought we could have been a bit more incisive, shown a bit more confidence possibly in the last third and picked the right pass.
"But in terms of how we played, we were totally dominant in terms of controlling the game."
Singling out Murray Davidson in particular, he added: "I cannot praise the players enough.
"Their attitude, their approach to it, I thought there were some really good individual performances."
Source: Team Talk
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