Yes this condition, as any gas related problems, is dangerous.

Your furnace is experiencing delayed ignition. This condition can be caused by improper gas pressure, a slow opening gas valve, a misdirected pilot flame or orifice, dirty or sooty orifices or burners, and drafts across the burners.

In typical fashion delayed ignition is usually marked with a loud bang or swoosh upon actually lighting.

Your furnace utilizes a pilot Re-ignition system. When your t-stat calls for heat the spark ignitor is energized along with the "pilot" gas valve. When working properly the pilot is quickly lit and the flame retification circuit shuts down the ignitor via the pilot flame and main gas valve opens and the pilot flame ignites the main burners.

Please contact a reputable, qualified service company and get it fixed. Don't be suprised if the suggest a new furnace as the pilot Re-ignition model is past its prime.

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