When travelling in Uruguay, you should always contact your intended destination in advance, whether it be a hotel, restaurant, winery, or travel service. While Uruguayans are not sticklers for having reservations, I recommend doing this for two reasons:
Unreliable "hours”(horarios) - Apart from hotels and larger restaurants, many shops or other services don't always stick to a very fixed schedule, and they may also vary their hours by season, or decide to close for a holiday break of a few weeks. Nothing worse than going out of your way only to find out that a place is closed... but at least you'll enjoy the journey!
Reservations in smaller locales – Outside of Montevideo and Punta del Este, smaller restaurants, cafes, or wineries may have limited space or inventory of supplies and they rely on confirmed reservations to manage their business for the day. You are likely to enjoy your experience more if you make a reservation in advance.
Uruguayans are always friendly and will try to accommodate you, but a phone call or message on social media in advance of your visit will greatly improve the experience. Note that most places in Uruguay have a Facebook page through which you can contact them, which is helpful if you don't speak Spanish or are outside of the country.