We Ask the Pros: Too Late to Buy Record-High Stocks?

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The stock market by virtually any measure begins the second quarter on Monday at all-time highs.

After teasing investors all last week, the S&P 500 finally closed at a record high ahead of the long holiday weekend—following the Dow Jones Industrial Average, which has been crushing its highs for awhile now.

In the first quarter, the Dow industrial average rose more than 11 percent—its best first quarter since 1998. The S&P 500's 10 percent increase and the Nasdaq Composite Index's 8 percent gain from January through March were those indexes' best first-quarter performances since 2012.

(Read More: Will the Jobs Report Keep the Stock-Market Bulls Running?)

With stock mutual fund inflows starting to pick-up, many individual investors are asking: Is it too late to buy this red-hot market? "Squawk Box" enlisted some Wall Street heavyweights to help answer that question. Here are their insights:

Jeffrey Solomon, CEO, Cowen and Company: "I think a lot of people have missed [the rally]. But you have to be measured about it, unemotional. If you're under-invested in the equity market, you've got to put a little money to work now. Dollar-cost-averaging is still a great way to make sure you don't market time. I'm not a great market timer. … We always have a 10 percent pullback. If you look at the statistics, once a year we're good for 5 to 10 [percent pullback]."

John Ryding, RDQ Economics chief economist and founding partner: "We were looking at 1,525 to 1,550 [on the S&P 500] for where the market might reasonably be at the end of the year. And for the third year in a row, we've been where we thought we'd be at the end of the year, pretty much at the end of the first quarter. Then the rest of the year has been a marking time. That has been the pattern in the markets."

Lee Partridge, Salient Partners chief investment officer: "I hate to go back to what we looked like in 2011 and 2012 as being indicative of what 2013 may look like. But you have a strong January-effect in both of those years. We rallied hard through the April-May time frame. And that classic adage, 'Sell in May, Going Away' would have been prescient advice as we hit the summer months. … I would wait for a bigger pullback. Ten to 15 percent would the magnitude that I'm looking for. People are always surprised by that, but it happens every year."

By CNBC's Matthew J. Belvedere; Follow him on Twitter @Matt_SquawkCNBC