I just tried this and it seemed to do a good job of splitting the output:

perl -e '$u = `uptime`; print join("\n",(split(/\s{2,}/,$u)));'
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which gave me:
1:19pm
up 3 days,
4:36,
2 users,
load average: 0.22, 0.31, 0.36

so if you had:

@uptime = split(/\s{2,}/,`uptime`);
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The part you want should be $uptime1 and $uptime2