It's generally not considered rude if someone takes a bit of time to decide what to order at a restaurant, especially during their first visit. Choosing a meal is a personal decision, and many restaurants have diverse menus with various options, making it perfectly normal for people to take some time to make their selection.
However, there are a few points to keep in mind to be considerate of the restaurant staff and other diners:
Be mindful of the situation: If the restaurant is particularly busy and the staff is rushed, it might be considerate to take a quicker look at the menu or ask for some recommendations to expedite the ordering process.
Be polite to the waiter: When the waiter comes to take your order, if you need a bit more time, simply smile and politely ask for a few more minutes. Acknowledge their presence and let them know you appreciate their patience.
Plan ahead: If you know you are going to a restaurant with an extensive menu, you can try to review the menu online beforehand. This can help you narrow down your choices and make the ordering process smoother.
Ask for recommendations: If you're having trouble deciding, don't hesitate to ask the waiter for suggestions based on their experience or popular dishes at the restaurant.
Be decisive after a reasonable time: While taking some time to decide is normal, try not to excessively delay the ordering process, as it can be frustrating for both the waiter and other diners waiting to order or be served.
In essence, as long as you are courteous, respectful, and not excessively indecisive, it is generally not considered rude to take some time to decide what to order at a restaurant, especially if it's your first visit and you're unfamiliar with the menu. Restaurant staff are accustomed to this and understand that customers may need a little time to make their choice.