I just received my second citi card, while activating I asked that they match the credit line on my first card (+10k), which they did within minutes.
If this is your first card, I would wait at least 3-4 months min; if you have addt'l accounts, just call the credit department (or customer service) and request the increase.
[4/24] Scores 8/9: 700-800s. Util: 1-2%. Inq/12: EQ 0, EX 3, TU 2. AoOA=15.8y, AoYA=8m.
TCL $678.5K: Personal $562.5K, Business $116K.